In Internet Explorer, Tools, IE Options, Advanced, Uncheck:
"Activate install on demand" [Other] , and, "Activate install on demand" [Internet Explorer]
Other than that I use AdAware SE, SpyBot SD, SpywareBlaster, AVG Free Home Edition anti-virus, and have used Zone Alarm Free edition.
I also use a combination of CCLeaner & EmpTemp to clean out junk files.