With PCs anti-virus and anti-spyware programs are necessary, as is a firewall, which is a security device that blocks hacker attacks and keeps them out of your computer system.
McAfee VirusScan, now VirusScan Plus, integrates antivirus, firewall protection and anti-spyware in one program.
Keep anti-virus and anti-spyware programs up to date and allow the programs to conduct full scans of your computer regularly.
Make sure you have an anti-spyware program and an anti-virus program running.
Naturally, you should have a reliable antivirus and anti-spyware program in place as some websites that offer free stuff will also contain viruses and other bad things.