Gary,
I believe I remember you saying that you used the AVG Free software, correct? While it is good, there are some important drawbacks to it, and in your current situation the biggest being the fact it does NOT protect you against Malware which is what the Trojan horses are. AVG Free only protects you from viruses. Here is a short explanation from a very reliable site I use, PC Review.
"The free version of AVG does not provide protection from spywares, Trojans, worms, and rootkits and as such you need to be careful while surfing the Internet. AVG free is effective only against viruses, but you can make good use of it if you avoid random Internet surfing. In effect, it means that while using AVG free, you will have to limit your Internet surfing to known, reputed websites where the probability of malicious software programs is a lot less."
There are a lot of removal tools out there, but as long as you are running without full protection, the malware can continue to latch itself onto sites you visit. Trojans do NOT replicate, but once one is there, they can continue to find 'doors' into your computer.
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The bond that links your true family is not one of blood, but of respect and joy in each other's life. Rarely do members of one family grow up under the same roof.-- Richard Bach [i]Illusions