How malaware spreads on your computer?

It may sound like the rantings of a conspiracy theorist, but even the act of visiting some web sites can infect your PC with spyware and adware. Not that it can happen transparently, but many people just don’t recognize the red flags even when they’re staring them in the face. Specifically, these are the “add-ins” employed by some web sites that provide custom cursors,
interactive menus, or other eye candy. While loading a web page, you may see a message asking if it’s OK to install some ActiveX gadget “necessary” to view the page (e.g., Comet Cursor); here, the answer is simple: no.

Just as many viruses are written to exploit Microsoft Outlook, most spyware and adware targets Microsoft Internet Explorer. By switching to a browser like Firefox, you can eliminate the threat posed by many of these nasty programs.