Computer Virus Resources

Windows Viruses

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Netsky sticks in my mind because it was the first time that a virus insulted other virus authors. This virus can spread in many different ways including a voluntary download. Anti-keylogger Antivirus software Browser security Internet security Mobile security Network security Defensive computing Firewall Intrusion detection system Data loss prevention software. New malware that potentially can cause damage has been reported and has spread globally. Also known as Downup or Downadup , Conficker is a worm of unknown authorship for Windows that made its first appearance in

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A few years later, in February , Australian hackers from the virus-writing crew VLAD created the Bizatch virus also known as "Boza" virus , which was the first known virus to target Windows In late the encrypted, memory-resident stealth virus Win Cabanas was released—the first known virus that targeted Windows NT it was also able to infect Windows 3.

Even home computers were affected by viruses. The first one to appear on the Commodore Amiga was a boot sector virus called SCA virus , which was detected in November Users would be required to click on a link to activate the virus, which would then send an email containing user data to an anonymous email address , which was later found to be owned by Larose. Data sent would contain items such as user IP address and email addresses, contacts, website browsing history, and commonly used phrases.

In , larger websites used part of the Win A viable computer virus must contain a search routine , which locates new files or new disks which are worthwhile targets for infection.

Secondly, every computer virus must contain a routine to copy itself into the program which the search routine locates. Infection mechanism also called 'infection vector' , is how the virus spreads or propagates. A virus typically has a search routine, which locates new files or new disks for infection. The trigger, which is also known as logic bomb , is the compiled version that could be activated any time an executable file with the virus is run that determines the event or condition for the malicious " payload " to be activated or delivered [43] such as a particular date, a particular time, particular presence of another program, capacity of the disk exceeding some limit, [44] or a double-click that opens a particular file.

The "payload" is the actual body or data that perform the actual malicious purpose of the virus. Payload activity might be noticeable e. Virus phases is the life cycle of the computer virus, described by using an analogy to biology. This life cycle can be divided into four phases:. The virus program is idle during this stage. The virus program has managed to access the target user's computer or software, but during this stage, the virus does not take any action.

The virus will eventually be activated by the "trigger" which states which event will execute the virus, such as a date, the presence of another program or file, the capacity of the disk exceeding some limit or the user taking a certain action e.

Not all viruses have this stage. The virus starts propagating, that is multiplying and replicating itself. The virus places a copy of itself into other programs or into certain system areas on the disk. The copy may not be identical to the propagating version; viruses often "morph" or change to evade detection by IT professionals and anti-virus software. Each infected program will now contain a clone of the virus, which will itself enter a propagation phase.

A dormant virus moves into this phase when it is activated, and will now perform the function for which it was intended. The triggering phase can be caused by a variety of system events, including a count of the number of times that this copy of the virus has made copies of itself. This is the actual work of the virus, where the "payload" will be released. It can be destructive such as deleting files on disk, crashing the system, or corrupting files or relatively harmless such as popping up humorous or political messages on screen.

Computer viruses infect a variety of different subsystems on their host computers and software. COM files , data files such as Microsoft Word documents or PDF files , or in the boot sector of the host's hard drive or some combination of all of these.

A memory-resident virus or simply "resident virus" installs itself as part of the operating system when executed, after which it remains in RAM from the time the computer is booted up to when it is shut down.

Resident viruses overwrite interrupt handling code or other functions , and when the operating system attempts to access the target file or disk sector, the virus code intercepts the request and redirects the control flow to the replication module, infecting the target. In contrast, a non-memory-resident virus or "non-resident virus" , when executed, scans the disk for targets, infects them, and then exits i. Many common applications, such as Microsoft Outlook and Microsoft Word , allow macro programs to be embedded in documents or emails, so that the programs may be run automatically when the document is opened.

A macro virus or "document virus" is a virus that is written in a macro language , and embedded into these documents so that when users open the file, the virus code is executed, and can infect the user's computer. This is one of the reasons that it is dangerous to open unexpected or suspicious attachments in e-mails. Email virus — A virus that intentionally, rather than accidentally, uses the email system to spread. While virus infected files may be accidentally sent as email attachments , email viruses are aware of email system functions.

In order to avoid detection by users, some viruses employ different kinds of deception. Some old viruses, especially on the DOS platform, make sure that the "last modified" date of a host file stays the same when the file is infected by the virus.

This approach does not fool antivirus software , however, especially those which maintain and date cyclic redundancy checks on file changes. They accomplish this by overwriting unused areas of executable files. These are called cavity viruses. Because those files have many empty gaps, the virus, which was 1 KB in length, did not add to the size of the file.

In the s, as computers and operating systems grow larger and more complex, old hiding techniques need to be updated or replaced. Defending a computer against viruses may demand that a file system migrate towards detailed and explicit permission for every kind of file access.

While some kinds of antivirus software employ various techniques to counter stealth mechanisms, once the infection occurs any recourse to "clean" the system is unreliable. This leaves antivirus software little alternative but to send a "read" request to Windows OS files that handle such requests.

Some viruses trick antivirus software by intercepting its requests to the Operating system OS. A virus can hide by intercepting the request to read the infected file, handling the request itself, and returning an uninfected version of the file to the antivirus software. The interception can occur by code injection of the actual operating system files that would handle the read request.

Thus, an antivirus software attempting to detect the virus will either not be given permission to read the infected file, or, the "read" request will be served with the uninfected version of the same file.

The only reliable method to avoid "stealth" viruses is to "reboot" from a medium that is known to be "clear". Security software can then be used to check the dormant operating system files. Most security software relies on virus signatures, or they employ heuristics. Most modern antivirus programs try to find virus-patterns inside ordinary programs by scanning them for so-called virus signatures.

Such a virus "signature" is merely a sequence of bytes that an antivirus program looks for because it is known to be part of the virus. A better term would be "search strings ". Different antivirus programs will employ different search strings, and indeed different search methods, when identifying viruses. If a virus scanner finds such a pattern in a file, it will perform other checks to make sure that it has found the virus, and not merely a coincidental sequence in an innocent file, before it notifies the user that the file is infected.

The user can then delete, or in some cases "clean" or "heal" the infected file. Some viruses employ techniques that make detection by means of signatures difficult but probably not impossible. These viruses modify their code on each infection. That is, each infected file contains a different variant of the virus.

One method of evading signature detection is to use simple encryption to encipher encode the body of the virus, leaving only the encryption module and a static cryptographic key in cleartext which does not change from one infection to the next. If the virus is encrypted with a different key for each infected file, the only part of the virus that remains constant is the decrypting module, which would for example be appended to the end.

In this case, a virus scanner cannot directly detect the virus using signatures, but it can still detect the decrypting module, which still makes indirect detection of the virus possible. Since these would be symmetric keys, stored on the infected host, it is entirely possible to decrypt the final virus, but this is probably not required, since self-modifying code is such a rarity that it may be reason for virus scanners to at least "flag" the file as suspicious.

This is called cryptovirology. At said times, the executable will decrypt the virus and execute its hidden runtimes , infecting the computer and sometimes disabling the antivirus software. Polymorphic code was the first technique that posed a serious threat to virus scanners.

Just like regular encrypted viruses, a polymorphic virus infects files with an encrypted copy of itself, which is decoded by a decryption module. In the case of polymorphic viruses, however, this decryption module is also modified on each infection. A well-written polymorphic virus therefore has no parts which remain identical between infections, making it very difficult to detect directly using "signatures". To enable polymorphic code, the virus has to have a polymorphic engine also called "mutating engine" or " mutation engine" somewhere in its encrypted body.

See polymorphic code for technical detail on how such engines operate. Some viruses employ polymorphic code in a way that constrains the mutation rate of the virus significantly. For example, a virus can be programmed to mutate only slightly over time, or it can be programmed to refrain from mutating when it infects a file on a computer that already contains copies of the virus.

The advantage of using such slow polymorphic code is that it makes it more difficult for antivirus professionals and investigators to obtain representative samples of the virus, because "bait" files that are infected in one run will typically contain identical or similar samples of the virus.

This will make it more likely that the detection by the virus scanner will be unreliable, and that some instances of the virus may be able to avoid detection. To avoid being detected by emulation, some viruses rewrite themselves completely each time they are to infect new executables.

Viruses that utilize this technique are said to be in metamorphic code. To enable metamorphism, a "metamorphic engine" is needed.

A metamorphic virus is usually very large and complex. As software is often designed with security features to prevent unauthorized use of system resources, many viruses must exploit and manipulate security bugs , which are security defects in a system or application software, to spread themselves and infect other computers.

Software development strategies that produce large numbers of "bugs" will generally also produce potential exploitable "holes" or "entrances" for the virus. In order to replicate itself, a virus must be permitted to execute code and write to memory. For this reason, many viruses attach themselves to executable files that may be part of legitimate programs see code injection. If a user attempts to launch an infected program, the virus' code may be executed simultaneously. This makes it possible to create a file that is of a different type than it appears to the user.

For example, an executable may be created and named "picture. The vast majority of viruses target systems running Microsoft Windows. This is due to Microsoft's large market share of desktop computer users. Many Windows users are running the same set of applications, enabling viruses to rapidly spread among Microsoft Windows systems by targeting the same exploits on large numbers of hosts.

While Linux and Unix in general have always natively prevented normal users from making changes to the operating system environment without permission, Windows users are generally not prevented from making these changes, meaning that viruses can easily gain control of the entire system on Windows hosts.

This difference has continued partly due to the widespread use of administrator accounts in contemporary versions like Windows XP. In , researchers created and released a virus for Linux—known as " Bliss ". Unlike Windows users, most Unix users do not log in as an administrator, or "root user" , except to install or configure software; as a result, even if a user ran the virus, it could not harm their operating system.

The Bliss virus never became widespread, and remains chiefly a research curiosity. Its creator later posted the source code to Usenet , allowing researchers to see how it worked.

Many users install antivirus software that can detect and eliminate known viruses when the computer attempts to download or run the executable file which may be distributed as an email attachment, or on USB flash drives , for example.

Some antivirus software blocks known malicious websites that attempt to install malware. Antivirus software does not change the underlying capability of hosts to transmit viruses. Users must update their software regularly to patch security vulnerabilities "holes". Antivirus software also needs to be regularly updated in order to recognize the latest threats.

This is because malicious hackers and other individuals are always creating new viruses. Secunia PSI [90] is an example of software, free for personal use, that will check a PC for vulnerable out-of-date software, and attempt to update it. Ransomware and phishing scam alerts appear as press releases on the Internet Crime Complaint Center noticeboard.

Ransomware is a virus that posts a message on the user's screen saying that the screen or system will remain locked or unusable until a ransom payment is made.

Phishing is a deception in which the malicious individual pretends to be a friend, computer security expert, or other benevolent individual, with the goal of convincing the targeted individual to reveal passwords or other personal information. Other commonly used preventative measures include timely operating system updates, software updates, careful Internet browsing avoiding shady websites , and installation of only trusted software.

There are two common methods that an antivirus software application uses to detect viruses, as described in the antivirus software article.

The first, and by far the most common method of virus detection is using a list of virus signature definitions. This works by examining the content of the computer's memory its Random Access Memory RAM , and boot sectors and the files stored on fixed or removable drives hard drives, floppy drives, or USB flash drives , and comparing those files against a database of known virus "signatures".

Virus signatures are just strings of code that are used to identify individual viruses; for each virus, the antivirus designer tries to choose a unique signature string that will not be found in a legitimate program. Different antivirus programs use different "signatures" to identify viruses. The disadvantage of this detection method is that users are only protected from viruses that are detected by signatures in their most recent virus definition update, and not protected from new viruses see " zero-day attack ".

A second method to find viruses is to use a heuristic algorithm based on common virus behaviors. This method has the ability to detect new viruses for which antivirus security firms have yet to define a "signature", but it also gives rise to more false positives than using signatures. False positives can be disruptive, especially in a commercial environment, because it may lead to a company instructing staff not to use the company computer system until IT services has checked the system for viruses.

This can slow down productivity for regular workers. One may reduce the damage done by viruses by making regular backups of data and the operating systems on different media, that are either kept unconnected to the system most of the time, as in a hard drive , read-only or not accessible for other reasons, such as using different file systems.

This way, if data is lost through a virus, one can start again using the backup which will hopefully be recent. Likewise, an operating system on a bootable CD can be used to start the computer if the installed operating systems become unusable.

Backups on removable media must be carefully inspected before restoration. The Gammima virus, for example, propagates via removable flash drives.

Many websites run by antivirus software companies provide free online virus scanning, with limited "cleaning" facilities after all, the purpose of the websites is to sell antivirus products and services. Shot in the dark: Easily one of the most famous and prolific variants of computer worms, famous for effectiveness and the fact that it was authored by an 18 year-old German, Sven Jaschan, who confessed to having written these and other worms.

Netsky sticks in my mind because it was the first time that a virus insulted other virus authors. Here the authors of both the Bagle and Mydoom worm families were dissed and, in some cases, Netsky included code that removed versions of the competing viruses. Though obviously, not a really good friend! Though I did consider the Morris worm, regarded as the first worm, I had to go with the Storm worm as the 5th to include. Known by many names the Storm Worm is a backdoor Trojan that affects Microsoft based computers.

The Storm Worm was a Trojan horse that would join the infected computer to a bot-net — a network of remotely-controllable computers. Though it was thought to be a bot-net of millions of computers, the exact numbers were never known. Flame is clearly the next evolution in computer viruses, and were I an Iranian scientist Flame would definitely be at the top of my list. Which are on your list? Talk Back and Let Me Know. Hackers swipe card numbers from local government payment portals.

Zero Trust technology works; excuses don't. Access to over 3, backdoored sites sold on Russian hacking forum. How to spot "deep fake" videos. From smartphones to securing IoT and smart cities. US Senate summons big tech companies over consumer data security. Analysis reveals that DDoS attacks against universities are probably the work of students. My Profile Log Out. Security Hackers swipe card numbers from local government payment portals. Security Zero Trust technology works; excuses don't.

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65 rows · The compilation of a unified list of computer viruses is made difficult because of naming. To aid the fight against computer viruses and other types of malicious software, many security advisory organizations and developers of anti-virus software compile and publish lists of viruses. When a new virus appears, the rush begins to identify and . See the latest information on computer virus attacks and their removal. McAfee is the leader in internet security and virus detection. Keep up to date on the most recent virus threats, recently discovered viruses and recently updated viruses. While some pranksters created virus-like programs for large computer systems, it was really the introduction of the personal computer that brought computer viruses to the public's attention. A doctoral student named Fred Cohen was the first to describe self-replicating programs designed to modify computers as viruses.