Generally, a Computer Virus is any program that is designed to replicate itself inside a computer or network, invade root programming to avoid being deleted, and cause damage to software.
Viruses are usually classified separate from malware, spyware, worms, and trojans; these are more usually designed to send information back to a source, and don't often directly interfere with computer function. Viruses, however, often have no other purpose than to cause problems; they have many infection strategies and can be classified many ways depending on definition. However, the most basic classifications would include:
- Hijacking virus: these take control of your computer functionality to perform a specific task, like emailing itself to your contacts or overwriting data
- Infector virus: these sit dormant in files until activation, and then affect files or data on the computer
- Macro virus: macros are small program codes which allow larger programs to perform tasks according to a specific pattern; their simplicity makes them easy to code for damage or other harm
- Logic Bomb virus: these are dormant until they are activated by the computer clock, allowing them to stay hidden even during a virus scan; their time-dependent functionality allows them to infect and attack many computers or networks all at the same time
Viruses and other harmful programs are evolving all the time as dedicated virus-programmers work to overcome better anti-virus technology. Most viruses are identified and protected against within a day or two; keeping your virus protection up-to-date is the best way of avoiding most viruses.