everyday
The programs should be running constantly in the background to protect your computer from infection while you're online or installing software. If you mean how often should you run a scan most programs will run one automaticaly by them selves once every month or week.

I would say once a month is fine and also immediately after removing any virus or malware but if you want to there's nothing stopping you from running them more often.

Hope that helps,
Bob
2 - 3 times a week.
You probably shouldn't do it less because almost every website you go to now has some sort of virus attachment.
If your one of those people who are on the internet a lot you may need to run an anti virus everyday. Other than that, 3 times a week should be fine.

Also, I would recommendnd Trend Micro. It's the best anti virus out there.

Hope I cold help in some way:)
-caitlan.
if you are not doing loads of work on a computer you might wanna check every morning or every evening before you close your pc.
Every day.

There are all kinds of vicious trojans and things lurking on the web sites.

Hackers are always trying to put things in too.

Your firewall will block them.
every day