Hi there
Don't worry too much. It's not a Trojan as such. Just a bit of malware. An inconvenience and very frustrating but not hard to get rid of.
Do as the others said and install Adaware or something similar. Every machine should have one of them installed and a scan run regularly.
Another way to clean up your system is by clearing out your cookies, temp, and temporary internet files on a regular basis. Doing that will also keep your system resources free and keep your pc ticking along more smoothly.
If you're comfortable working in the registry do check your running processes for anything unusual (don't delete anything if you're unsure of what it is).
Go to Start>Run>type in regedit and hit OK>
Go to HKEY_LOCAL_MACHINE>Software>Microsoft>Windows>Current Configuration>Run .... Most virus's can be found in there because they want to run on startup. Deleting them from there won't get rid of a virus though. You need to find out where the main virus files are. They're usually embedded in your Windows system files.
If you don't have up to date Anti Virus software running and you're able to get online, go to
www.trendmicro.com and run their free online virus scanner. They can usually clean a virus off your system but if they can't they will tell you exactly how to do it yourself. Print out and follow their advice exactly!
Again, don't delete or modify anything in your registry if you're unsure of what it is or does. I recently did a repair job for a customer after she'd let her sister try to fix things. A two hour job. I could have fixed the original problem in 10 minutes.
Sorry to be so long winded. I tend to do this when I'm trying to help. My customers' eyes simply glaze over.
Cheers!
kiri