Instead of sending viruses through e-mail messages, attackers now make use of legitimate websites. Codes capable of triggering silent virus downloads can be embedded in pictures, advertisements or even seemingly blank areas at the bottom of the page.

When users click on the items or simply move their mouse over the virus-laden area, the download begins.

Earlier this year, several sites related to the world's most popular online role-playing game, World Of Warcraft, reported similar attacks.

Trading of weapons or gold in various online games is now so popular that some hackers have started exploiting this virtual economy.

When trading, some players hide a virus within the items for sale or embed them in files sent to the other user. These viruses may then give online criminals backdoor access to your computer, or record keystrokes of, say, passwords to your online bank accounts or game accounts.