Computer viruses can wreck havoc to the operations of the computer. A computer virus is a type of malware that is intentionally written to gain entry into your computer, without your knowledge or permission. It has the capacity to modify or replicate itself, in which case it will continue spreading. There are varying different types of computer viruses and their effects also vary widely. While some simply replicate themselves, others adversely affect the programs and consequently, the system’s performance. This therefore underlines the importance of not assuming that the virus is harmless and leaving it in the system. It is important that you scan your computer for viruses once in a while, so that you can be sure about its protection.
There are various types of computer viruses, classified in terms of techniques, origin, the types of files affected, damage, OS or Platform attacked, as well as the places they hide. It’s relatively hard to answer how how many different types of computer viruses there are but below covers the main core concepts of the common types:
Resident viruses: These are permanent viruses dwelling in RAM memory. In this case, they would be in a position to overcome, as well as interrupt, all operations that the system executes. Their effects include corrupting programs and files that are closed, opened, renamed or copied.
Overwrite viruses: These viruses delete information that is in the infected files. In this case, the infected files would be rendered totally or partially useless. Unfortunately, you would only clean the infected file by deleting it completely, therefore losing original content.
Direct action viruses: This virus replicates itself, then acts when executed. Subject to satisfaction of particular conditions, the virus infects files located in the folders or computer directory. It is also in directories specified in the AUTOEXEC.BAT PATH. In most cases, it is located in hard drive’s root directory and takes particular action when the computer boots.
File infectors: This virus infects executable files or programs. On running the programs, the virus would be activated, then be able to carry out its damaging effects. Most of the existing viruses are in this category.
Boot viruses: This virus infects the hard disk’s or floppy drive’s boot sector. This would make the computer unable to boot. These viruses can, however, be avoided by ensuring that the floppy disks and hard drive is well protected. Never start the computer using an unknown disk drive or floppy disk.
Directory viruses: This virus alters the paths indicating a file’s location. In this case, when the infected program is executed, you will be running the program unknowingly, since the virus has moved the original program and file to another location. This therefore makes it impossible to locate the moved files.
Macro virus: This virus affects files created using particular programs or applications containing macros. The mini-programs increase their ability to automate some operations, in which case they would be performed as single actions. The user would therefore be saved the trouble of executing them singularly.
The most common types of viruses seen in 2014 – 2015 that have a high impact on users are Browser Highjack viruses. Generally this type of infection is not really a virus but something called PUP or Potentially unwanted software. In most cases these browser highjacks change the users home page and search settings in the web browser and often make it extremely hard to remove and restore the default settings. Often times these kinds of browser highjacks get installed from bundled software that may include free programs such as computer games or wall papers.
There are numerous other types of computer viruses, as they are constantly being created. It is always important that you ensure that you are using an active antivirus client that is is updated so it can be effective against new computer viruses.
Refer to http://www.removevirus.org/virus-definitions/ for a list of well defined viruses.