Download AVG Free Edition, and set it up to scan your computer once a day.

If you can pay some $$, try Kaspersky or Trend Micro. Each has a 30 day free trial. Both check for Adware - which makes a back door for tracing your surfing habits.

Spybot Search and Destroy is good and free. Careful - there is another one that looks a lot like the same name...but charges money!

Spam? PM me and I can pass on some tips that help! Too long to add here.