Virus not marked as high-spam

[Dave]

I've had quite a few emails in the last couple of days that were marked as
having  'Virus (Trojan.Downloader-648)', and blocked by clamav, bitdefender and
mailscanner:
ClamAV: Full Text.exe contains Trojan.Downloader-648
Bitdefender: Found virus Trojan.Peed.A in file Full Text.exe
MailScanner: Executable DOS/Windows programs are dangerous in email
(Full Text.exe)
No programs allowed (Full Text.exe)

All of these have been marked as high-spam and blocked completely, which is
good. I had 1 this morning though that was marked only as spam, and therefore
sent a pickup notice to the end-user, even though clamav & bitdefender had found
the virus in it and blocked the message.

These messages all have a variation of news items:
Sadam Hussein alive!
Chinese missile shot down Russian aircraft
President of Russia Putin dead.
Hugo Chavez dead. (which is the one that slipped through)

Any ideas how to make sure that doesn't happen?