Viruses

A virus is a type of software that generally is malicious to your computer. They can get into your computer in many ways. A common way that viruses get into your computer is by downloading random ads from unsecure webpages (such as the ones that offer you free emoticons etcetera) by downloading torrents, usin P2P software, and generally downloading things from the internet.

There are many different types of viruses, one type is the trojan, that gets into your without you noticing. The files of the virus sometimes store themselves in the hidden files of your computer, so to remove them you have to make them visible. Viruses sometimes change things of your computer, sometimes are pranks, and sometimes they try to steal information from you (spyware). If i remember correctly, the first viruses were installed from software you boguht legitimally, and it was done so that the same company sell you the anti virus.

If you want to avoid viruses you may buy a good antivirus such as norton, panda, Mcafe, Avira or Nod32. However, this antiviruses are really expensive, but it is better to buy them than just wait your computer to brake down.