You're looking for a good antivirus?
that doesn't cost any money?
that's widely accepted so that you can look up forums for support?
Avira Antivir Personal Antivirus is an excellent option for you.
I'd say the most famous free antiviruses are Avira, AVG, and Avast.
Avira gets a good rap on the internet and can hold its own. There are technical analyses which explore how many bits of malware it can find, etc., and it is claimed that the results are better than some of the paid antiviruses.
Avira do offer higher levels of antivirus for which you have to pay, so obviously they will be more powerful.
Give the free version a try so that you can check out the company. They are quite up-front on the features you don't get in the free version. If you like the experience you can always upgrade then.
Go here to learn more Avira Antivirus Free Download