However, instead of spreading from file to file, they spread from computer to computer, infecting an entire system. The rise in Internet use is paralleled by an increase in Internet-borne malicious code carried by Microsoft ActiveX controls and Sun Microsystems Java applets. Although it has not yet happened, it is possible for virus writers to use ActiveX and possibly Java to introduce viruses, worms and Trojan horses onto a web-surfer's computer, turning Web pages into virus carriers. By simply surfing the Web, users could expose their computer to viruses spread via ActiveX controls, without downloading files or even reading e-mail attachments. The virus writers could then use the virus to access RAM, corrupt files, and access files on computers attached via a LAN, among other things.
Viruses are either benign or malignant .
The majority of viruses are harmless and do no real damage to a computer or files. A benign virus might do nothing more than display a message at a pre-determined time or slow down the performance of a computer. Malignant viruses cause damage to a computer system, such as corrupting files or destroying data. Just because a virus is classified as malignant does not mean that the damage it causes is intentional. Sometimes the damage is the result of poor programming or unintended bugs in the viral code.