Hi Doris.
I think ya might have Trojan Downloader.
It was probably on your PC before installin Yahoo Antispy. conflicts.
Do ya have Ewido anti-trojan scanner free for pesonal use. Alot of use here are using it.
http://www.ewido.net/en/
Ya should send us a HiJack This Log file I think ya just copy and paste it.
HiJackThis is a safe program no intstall. It shows all running processes in detail.
http://www.download.com/HijackThis/3000-8022_4-10307556.html
Someone here might know whats happen if ya paste the log file.