I’m starting a small computer repair business, and I offer free avast! installs. Is it legal for me to use your logo on my website? The last thing I want to do is violate a copyright, and I wondered if you had a policy about it. I couldn’t find one.
It is fine to use a avast logo on your website, but make it a link to the avast website.
That’s great! Thanks for the fast reply too. 
Perhaps this is also something to consider:
http://www.avast.com/affiliates
Wow, talk about helpful!