A Virus will usually be pretty noticable, but there are viruses that try to run in the backround and stay hidden. If your computer
is extremely slow, one possibility is a virus. I would suggest avg if you need a free virus program.
Avg free antivirus download.
Most computers will come with a virus protection program though. Make sure you run a virus scan often. Also, it is important that
your virus definitions are up to date before scanning. Your scan could miss a potential problem if you don't update the virus
definitions. We recommend running a full system scan every few weeks. We also recommend running a spyware check as well every time
you run a virus check.