The antivirus product can be tricked into not scanning potentially malicious files.
The remote host is running the ClamAV antivirus client version. This version of ClamAV is vulnerable to a flaw where file scanning can be bypassed by passing malformed MIME-encoded requests. An attacker exploiting this flaw would be able to send malicious files through the antivirus product without detection.
Upgrade to version 0.88.7 or higher.