Once you get rid of any nasties, you may consider switching to Firefox or some alternative browser. Internet Explorer has had a very bad security track record for many years now, so why make it even harder for yourself to keep your computer clean? And now we learn there is another fresh load of vulnerabilities just announced this week, so here we go again...
I have had no viruses and no spyware on my Windows computer, not in the last nine or ten years, and these are the general rules to work safely.
[i] Always apply current patch (service pack) upgrades *without fail*. This is the primary means of defence.
[ii] Configure the system to run only the services that are really required. Unnecessary services are the enemy of good security.
[iii] Never connect the computer to the internet without using a properly configured firewall. For double protection use an intrusion detection system.
[iv] Never never use MS Outlook as your mail client. This program has the track record of being the most effective vector for viral transmission on the planet; there are many alternatives such as Mozilla and Eudora that are not so prone to transmitting viruses.
[v] Avoid MS Internet Explorer. Many of the vulnerabilities in Outlook have also affected this web browser. The new Firefox browser is very nice, and considerably less risky, so maybe you could try that. http://www.getfirefox.com
[vi] Be aware of unsafe behaviour -- i.e. never open mail attachments unless you know and trust exactly who they are from, blah blah, don't download and run software from unknown sources, yik yak...
[vii] Use an antivirus scanner and keep the signature files up to date. In fact, for modern viruses, this is now one of the least efficient lines of defence -- by the time the AV company has released new sigantures for a new virus, *millions* of computers on the net that are not subject to measures i-vi can be infected. And a lot of viruses simply disable or bypass AV tools. These days, a non-patched, non-firewalled computer will be infected on average within 20 minutes. A typical antivirus update can be hours or even days late before it takes account of the new risk.
[viii] Set aside a regular time to do routine system maintenance -- back up your documents and spreasheets etc, but also run a spyware checker. It should only take half an hour per week, and you can do it while you are checking your email or whatever.
We were having discussions about all of this over in the Computers and Internet forum, if I can be of any further help...
Good luck with it.