No! Compressed or encrypted files cannot be read by antivirus systems while being transmitted. To mitigate this risk, antivirus agents are installed on systems so that when the files are uncompressed or un-encrypted they are then scanned.
For more information on this topic, visit these other SearchSecurity.com resources:
News & Analysis: Scanning encrypted e-mail a tricky proposition
Ask the Expert: Detecting viruses in encrypted files
News & Analysis: Heuristics brings intelligence to virus fight
This was first published in October 2002