As usual, many of the self-proclaimed "security experts" here are giving out terrible, potentially harmful advice. Ignore these pimply-faced individuals, many barely past puberty, typing away on a computer that Mommy and Daddy
bought for them.
ClamWin is an on-demand scanner only. Your computer does not even know it is there until you are actively running a scan.
Avast, in addition to being able to run a traditional full system scan for malware (after the fact)... also has real-time, resident protection to stop infections BEFORE they hit your hard drive.
ClamWin will provide you with a decent "2nd opinion" if Avast catches something. False-positives DO exist! It is always best to double check before deleting a file that any A-V app says is infected. The chance always exists that the file that you allow it to delete is a needed system file.
In short, the avast! and Clamwin combo will give you pretty decent (not world-class) protection for zip...nada...nothing. I have used the exact same set-up, here in the past.