Anti-virus protection
You need anti-virus protection to monitor for viruses that might come into your PC through E-mail or internet browser or CD/DVD etc. You need access to the latest virus database at any time because virus programmers are constantly finding new ways into your PC. You need to be able to run virus scans on all hard drives, or selected folders, or just selected files.

AVG anti-virus

Is FREE for personal use and after trying many other products I prefer it. It does the job of protecting against all the things mentioned above and works in the background without bogging down your processor time. It is very useful to be able to select your own folders or just files (even one file) to scan as full system scans can take quite a while. AVG enables you to update your virus database at any time and automatic update schedules can be setup. The protection of E-mails in and out is live and very reassuring.
Do a full system scan whenever you have time to let it run - but at least once a week.
Make sure your virus database is up to date. Viruses are made daily.