Apache Redirect Useragent?

[JAB Creations]

I want to be able to detect a useragent string and redirect to a specific file for all requests. Anyone seen this sort of method of creating an apache useragent whitelist?

[Span]

It's not too hard to detect a useragent string and redirect it somewhere. A lot of us do that every day. Creating a useragent whitelist however is something different.

I mean, looking only at those user agent strings won't tell you anything about what it is doing:

Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)
Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)
Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)

They look okay and should be on your whitelist, but what if someone uses one of those strings to spam your guestbook or downloads your entire site three times a day? Or uses it for referral spam or harvest email addresses?