lucy24 - 8:42 pm on Apr 12, 2013 (gmt 0)
These are technically not 404 errors, as the server would deliver a '200 ok' since they are showing up,as real visits in your stats.
That's the default behavior. But if you turn off AcceptPathInfo, they will become 404s.
The OP said
all of which are using "Other Agent (unknown platform)" as the type of browser
I assumed you were talking about a literal string here. You can block by User-Agent. The easiest way is to use mod_setenvif in conjunction with mod_authz-whatsit:
BrowserMatch "Other Agent" keep_out
(listing all the browsers you unconditionally dislike, one per line)
Deny from env=keep_out
in the same place you list your IP lockouts.