I have found that avast home edition can’t detect the basic type of trivial( overwriting virus for com files ). I installed a winrar from a CD, the software was marked clean by avast, but when it was scanned with bitdefender av the setup file contained win32/cih.gen virus. so this too was not caught by avast.
Could be - in that case, submit the sample of the virus to virus@avast.com.
On the other hand, judging by the name (win32/cih.gen), it may also be a false positive from bitdefender.
You could also check the offending/suspect file at: Jotti - Multi engine on-line virus scanner if any other scanners here detect them it is less likely to be a false positive. You can’t do this with the file in the chest, you will need to move it out.
Or VirusTotal - Multi engine on-line virus scanner