From 50_scores.cf:

> # highly generic tests for viruses that are scored just high enough to run
>
> score MICROSOFT_EXECUTABLE 0.100
> score MIME_SUSPECT_NAME 0.100

The first one is exactly the same as your rule.  Raise the score if you wish.

Note that it's not KLEZ, but any MS executable.

Does this solve your problem?

Indeed, this is a bug -- spamassassin 2.55 is skipping non-text MIME parts even
in "full" tests.  You can see this easily by making a rule that matches
everything and running spamassassin -t -D rulesrun=255 to see what's being matched:

full TESTING123 /.*/s
describe TESTING123 testing 1 2 3 testing
score TESTING123 123

The above rule matches the entire message.  But the debug output shows that the
matched string has the non-text MIME parts elided.  Here's an excerpt:

...
--FHh3uZg20E616qMK8
[skipped audio/x-wav attachment]
--FHh3uZg20E616qMK8
[skipped application/octet-stream attachment]
--FHh3uZg20E616qMK8
[skipped application/octet-stream attachment]
...

To further confirm this, try a rule that matches the string "skipped".
It will actually match these "[skipped ... attachment]" strings.  Example:

full TESTING123 /\[skipped.*\]/
describe TESTING123 testing 1 2 3 testing
score TESTING123 123

debug: Ran full-text regex rule TESTING123 ======> got hit: match='[skipped
audio/x-wav attachment]'

sa doesn't act on binary attachments (unless a MUA will display them as readable
text, ie. they can act as a spam payload).  The performance hit of applying the
sa ruleset to binary attachments is huge, so we disabled it a long time ago.

You're much better off using a virus scanner -- or even a procmail rule -- to do
this.  SA is not a virus scanner, it's a spam scanner, that's its aim.

However the doco is misleading; it states that "full" applies to attachments as
well. so we should fix that.

My rule doesn't need the body of the attachment to be scanned.  It's enough if
the mime headers for the attachment are scanned.
 
Sure, email worms/viruses technically are something worse than spam, but there's
not much practical difference, especially when you're using GNU/Linux and thus
your system isn't vulnerable to the viruses anyway.  Viruses are just more junk
clogging up my mailbox.
 
If mime headers could be scanned, this rule would catch most viruses that are
currently around -- it used to work in SpamAssassin 2.43, but broke when I
upgraded to 2.55:
 
full IE_VULNERABILITY      
/Content-[Tt]ype:\s+(application.octet-stream|audio.x-midi|audio.x-wav|application.x-msdownload);\s+[Nn]ame\s*=.[^\n]+\.(exe|pif|scr|bat)/s
describe IE_VULNERABILITY   Exploits an IE bug
score IE_VULNERABILITY  150

1) full didn't used to allow access to attachments
2) 2.70 does, at least so far. :)