Sometimes it is obvious that you have picked up a virus on your computer.
For example, your e-mail contacts may inform you of strange messages coming from your address or your antivirus software may suddenly fail to start.
Sometimes, however, it is less obvious.
If any of the following seems familiar, your computer may have contracted a virus.
Are you getting unexpected messages, or are programs starting automatically?
Viruses can damage important Windows files or even some of your own programs. The results of this damage may cause strange messages to pop up on your screen, programs to start or close down on their own, or even cause Windows to shut itself off.
Is your computer running very slowly?
A virus will commonly cause much slower than normal computer performance. There can however be other reasons for slow performance, including a badly fragmented hard drive, a computer that has insufficient memory (RAM), or the existence of Spyware or Adware.