This is quite possibly not a security issue, but for me it is, cause spam is a security issue and an ugly on too, causes my server to bend over sometimes.
So, there's a number of spammer bots that leaves only text/numbers strings as user agent in my server log. So, is there a rule I could use to deny or redirect those cases?
A few examples:
dtrehrtsjmnd sy7bivetsl bvQdsltldp s
fdbdjf8 gq djvbkmxdr kqhjfxsfkjn
vsraskylubfldkmpsslidaisvlxsxcfhiyqbwap
aqfmefokp skhsauvaoxfywmbabkkvhafcxe h
As appose to normal strings like:
(compatible; Mozilla/5.0; MSIE 5.0; FAST Crawler 6; +http://www.sesam.no/bot/)