listname-request currently generates an auto-ack message.  This can be
done by the kinds of viruses that "spoof" the FROM: field resulting in
unwanted mail to the FROM address (if it really exists), of if does not
exist, a bounce back to the listowner.

I recommend as a reduction technique, updating your list's template

 >>> REQACK1 Your message to &LISTNAME-request@&MYHOST
.qq
[the rest of the original template]

Obviously this doesn't solve the problem of spam to the -request address.

Though I've never tried it (and it may have unintended bad consequences,
esp for non-SPAM mail), you could make all list-owners QUIET

OWNER= quiet:,[log in to unmask]

/Pete