HELP-IE HOME PAGE LOCKED

My IE homepage has been locked by an "anti-spyware" homepage. Every time I change back to my original or default homepage, it is automatically switched back to the anti-spyware home page. I guess my computer is being infected by this stupid web which says my computer was infected by a spyware and ask me to buy their product. Is there anyway I can find it and delete it? thanks for expert's advise.