The Lanap BotDetect APS.NET CAPTCHA component before 1.5.4.0 stores the UUID and hash for a CAPTCHA in the ViewState of a page, which makes it easier for remote attackers to conduct automated attacks by "replaying the ViewState for a known number."
https://exchange.xforce.ibmcloud.com/vulnerabilities/27409
http://www.vupen.com/english/advisories/2006/2518
http://www.symantec.com/enterprise/research/SYMSA-2006-005.txt
http://www.securityfocus.com/bid/18315
http://www.securityfocus.com/archive/1/438159/100/0/threaded
http://securitytracker.com/id?1016371