enigma1 - 10:24 am on Jul 3, 2010 (gmt 0)
$ua->agent('Casper Bot Search'); ........ etc.
Looks like a classic hack attempt.
example: vulnerable local script contains code
Attacker synthesizes user agent code (sample you may see in the server logs not encoded they use all kinds of things)
it is then utilized with a server request from the attacker:
executing the php code or try to see if the scripts disclose any other info.
I hope you get the idea and this is not original by any means there lots of discussions over the web if you want to search in depth. The code logged as a UA can have many variations.
Also they're trying different combinations based on server type and application language.