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A computer virus is a piece of malicious code that is prepended or appended to existing files on your computer. Viruses are named after biological viruses because they use similar techniques to spread from one place to another. “Virus” is often misused to refer to any threat. This usage is gradually being replaced with a more accurate term, "malware" (malicious software).

Computer viruses primarly attack executable files and documents. In short, this is how a computer virus works: after running the infected file, the malicious code is called and executed before the execution of the original application. A virus can infect any files that the current user has write permissions for.

Computer viruses can range in purpose and severity. Some of them are extremely dangerous because of their ability to delete files purposely from the hard drive. On the other hand, some viruses do not cause any damage – they only serve to annoy the user and demonstrate the technical skills of their authors.

If your computer is infected with a virus and cleaning is not possible, submit it to the ESET Research Lab for perusal. In certain cases, infected files can be modified to such an extent that cleaning is not possible, and the files must be replaced with a clean copy.