Back Up before installing any new software, regardless of the source.

Scan all floppy disks, CD-ROMs, and DVD-ROMs before using them in your computer. You never know if a nasty virus is lurking on a seemingly innocent disk.

Don't install pirated software onto your computer. Illegal copies of software, those downloaded from hacker websites or sourced from file-sharing programs often contain hidden viruses.

Before installing any software, be sure you know exactly what is being copied onto your system. Sometimes seemingly-innocent software can contain viruses or Trojans that can take control of your computer. This is a particular danger with file-sharing programs that allow you to trade MP3s, videos, etc. such as Kazaa, eDonkey.