Adware and Spyware
Ad ware and Spy ware are extremely common. 9/10 computers have been infected with spy ware. Spy ware collects personal data and files, which include your passwords and credit card numbers. Ad ware basically displays advertisements and can slow down your computer:
It is recommended to have two Anti spy ware programs. The two I use are:
Microsoft Anti-Spyware
Lavasoft Adware
Warning: Microsoft anti spy ware is beta and is a pre release of the product.
In addition, you could use these:
• Spybot
• Spy ware Doctor
All are free.