For someone that is concerned with verifying file checksums, state sponsored attacks, etc... 
I'm surprised you are using Avast! Good antivirus, but I had to remove it when they started snooping on users encrypted traffic. 
(MITM traffic interception using pre-installed certificates)

Heres a good write-up for anyone interested: 
http://www.thesafemac.com/avasts-man-in-the-middle/