How malaware spreads on your computer?

Napster started the P2P file-sharing craze years ago, but modern file sharing goes far beyond the trading of harmless music files. It’s estimated that some 40% of the files available on these P2P networks contain viruses, Trojan horses, and other unwelcome guests, but even these aren’t necessarily the biggest cause of concern.

To facilitate the exchange of files, these P2P programs open network ports and create gaping holes in your computer’s firewall, any of which can be exploited by a variety of worms and intruders. And since people typically leave these programs running all the time (whether they intend to or not), these security holes are constantly open for business.

But wait...there’s more! If the constant threat of viruses and Trojan horses isn’t enough, many P2P programs themselves come with a broad assortment of spyware and adware, intentionally installed on your system along with the applications themselves. Kazaa, one of the most popular file-sharing clients, is also the biggest perpetrator of this, and the likely culprit if your system has become infected with spyware. (Note that other products like Morpheus, BearShare, Imesh, and Limewire do this, too, just in case you were thinking there was a completely “safe” alternative.)