Adware

• Software on your computer that shows you advertisements such as pop-ups is called adware. Adware is commonly bundled with free software that is downloaded by computer users. The person who developed the free software is now trying to sell you a product.
  
  

Spyware

• Spyware is software that will spy on you and reports your computer and Internet usage. Reports may go to a company or individual who then sells this information to advertisers. In many cases, adware will also function as spyware. Spyware can also be downloaded with free software, and in some cases it installs itself from the Internet without your knowledge.
  
  

Computer Virus

• A computer virus is a malicious program designed to spread from computer to computer. Viruses may cause serious damage to your computer's files and functioning. Viruses are commonly spread through email attachments. Once your computer is infected, the virus may send email to your contacts without your knowledge.