The cryptographic module in ScatterChat 1.0.x allows attackers to identify patterns in large numbers of messages by identifying collisions using a birthday attack on the custom padding mechanism for ECB mode encryption.
http://www.securityfocus.com/bid/19485
http://www.securityfocus.com/archive/1/443038/100/100/threaded
http://www.scatterchat.com/advisories/2006-01_tech.html