can u tell ,if no read here:
A computer virus is an infiltration which corrupts existing files on your computer. Viruses are named as such after biological viruses, as they use similar techniques to spread from one computer to another.
Computer viruses attack mainly executable files and documents. To replicate, a virus attaches its "body" to the end of a target file. In short, this is how a computer virus works: after execution of the infected file, the virus activates itself (before the original application) and performs its predefined task. Only after that, the original application runs. A virus cannot infect a computer unless a user (either accidentally or deliberately) runs or opens the malicious program by him/herself.
Computer viruses can range in activity and severity. Some of them are extremely dangerous because of their ability to purposely delete files from a hard drive. On the other hand, some viruses cause no real damage – they only serve to annoy the user and demonstrate the technical skills of their authors.
It is important to note that viruses are (when compared to trojans or spyware) gradually becoming more of a rarity, since they are not commercially enticing for authors of malicious software. Also, the term "virus” is often incorrectly used to cover all types of infiltrations. At present, this is gradually being overcome and the new, more accurate term "malware” (malicious software) is used.
If your computer is infected with a virus, it is necessary to restore infected files to their original state – i.e. to clean them by using an antivirus program.
Examples of viruses are: OneHalf, Tenga, and Yankee Doodle
