i suggest you use a firewall that blocks OUTGOING connections.
windows firewall doesnīt block by default, it can do it, but that requires a lot of manual configurations by creating rules.
there are FREE really good firewalls available,
take a look at this list :
Results and comments - www.matousec.com
Comodo & Pc-Tools are at the top...
BUT, if you choose Comodo, do *NOT* install the "hopsurf-toolbar" !
itīs considered a security risk by experts, (fx. Corrine) and since itīs prechecked when you install, you *MUST* uncheck those 3 "options".
i really recommend it, have used it on Windows 7 since Windows 7-beta,
works great and also has Defence+, that keeps an eye on every program that wants to run.
also get Winpatrol, which is a "must have-program", itīs a free program that also monitors your PC.
itīs recommended by experts, (Corrine).