Computer viruses are just one kind of malware mal-icious soft- ware. Here are some of the other, most common kinds:. To recap, viruses are just one of several kinds of malware out there. They are manufactured, often with great care, intentionally targeting computers, systems and networks. Legalize marihuana! Sadly, not all viruses are so cuddly. Wifatch which appears to do nothing other than keeping other viruses out of your router. But still, there are far better ways to secure your router — and even the creators of Linux.
Wifatch tell you not to trust it. Some virus creators argue they make the world safer by pointing out security gaps and flaws that can be exploited by other viruses with truly malicious intentions. Email is one of the favorite means of transportation for computer viruses everywhere. You can get computer viruses through email by:. Instant messaging IM is another means for viruses to spread.
Skype, Facebook Messenger, Windows Live Messenger and other IM services are inadvertently used to spread viruses to your contacts with infected links sent through chat messages. Peer-to-peer file sharing services like Dropbox, SharePoint or ShareFile can be used to propagate viruses too. These services sync files and folders to any computer linked to a specific account, so when someone inadvertently or otherwise uploads a virus-infected file to a file-sharing account, that virus gets downloaded to everyone else with access to that shared folder.
Some file sharing services, such as Google Drive , scan uploaded files for viruses although it only scans files smaller than 25MB, giving virus spreaders an easy out — they just have to make sure their virus-infected files are larger than that. Fake antivirus infections are one of the most common types of virus-loaded software downloads. Last but not least, one of the most common yet most often overlooked means for viruses to spread is unpatched software. Virus introduced to system b. Trojan activated c. Logic bomb activated d.
Examples of Malicious Computer Programs
Destructive part of virus activated V Most Common Viruses a. Jerusalem virus b. Cascade virus c. Brain virus d. Italian virus e. What are they Free Essays words 7. A lengthy and informative description of the evolution and history on microcomputer viruses will be given, to give you a background of their origin for some understanding of how they came to be. The next segment in the report is on how to combat computer viruses with the development of anti-virus applications.
The current status of microcomputer viruses will also be discussed, naming the most common types of viruses and the most harmful type at this present point in time Free Essays words 5. A computer virus is a piece of malicious code that is capable of copying itself and typically has a detrimental effect such as corrupting a system or destroying data. Computer viruses are written with the sole intention of stealing data or crippling a system. The term computer virus is derived from and is in some sense analogous to a biological virus.
The word virus itself is Latin for poison. Better Essays words 4. Therefore, the answers are argumentatively acknowledged by the different authors and explanations of the consequences in causing computer viruses. The paragraphs are mainly focused in four areas, the causes of computer viruses, the economic impacts on government intelligence nuclear, also stealing sensitive information.
On page one of Dr Solomon's Virus Encyclopaedia , the undesirability of viruses, even those that do nothing but reproduce, is thoroughly explained. An article that describes "useful virus functionalities" was published by J. Gunn under the title "Use of virus functions to provide a virtual APL interpreter under user control" in 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 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 a logic bomb , is the compiled version that could be activated any time within an executable file when the virus is run that determines the event or condition for the malicious " payload " to be activated or delivered  such as a particular date, a particular time, particular presence of another program, capacity of the disk exceeding some limit,  or a double-click that opens a particular file.
The "payload" is the actual body or data that performs 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. 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.
How to Prevent a Computer Virus from Ruining Your Day
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. EXE or. 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 viruses are viruses 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. They generally target a specific type of email system Microsoft's Outlook is the most commonly used , harvest email addresses from various sources, and may append copies of themselves to all email sent, or may generate email messages containing copies of themselves as attachments.
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 files that handle such requests. Some viruses trick antivirus software by intercepting its requests to the operating system. 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. 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.
Catch me if you can
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.