Most of the time, suprisingly, a virus must have your permission to infect your computer. One of the primary ways this happens is through email attachments and downloaded programs and files. The really bad part is that even email you receive from a friend might be infected with a virus either because they did not realize it or because the virus is a type that actually sends itself out to everyone in your friends address book. 

Another threat is pop-up ads. They are slowing becoming less of a nuisance and a threat as technology advances, but these are still a major source of viruses and spyware. The reason is that these messages that pop-up from malicious websites can be very clever at tricking you into thinking it is actually a message produced by your own computer or that it is something you might actually want. It is important that you spend some time scrutinizing these messages before clicking on them even though our own computers often train us to just click "OK" and move on.

Pop-Up Ads 

The first recommendation to prevent pop-up ads and the viruses they might carry is to download the latest version of Microsoft Internet Explorer or use Mozilla's Firefox browser which have very effective pop-up ad blockers built in. 

However, if you can't install another browser or still encounter the occasional pop-up ad it is important to recognize them as pop-up's and not system messages like the one below:

If you do encounter a pop-up ad it is important to not click anywhere inside of it, but use one of the following techniques to close it:

• Click the "X" in the upper right corner
• On the "Start" bar right click on that window's tab and choose "Close"
• Press "Alt" and "F4" together to close the window

Email Attachments

Attachments to email can carry viruses and even if they come from a friend they can still be infected.

Making sure you have a good anti-virus program running or use an internet based service such as Google's Gmail that has anti-virus protection built in.