While as a home user you may have not dealt with Citrix much, it is quite popular in business environments, especially in places where people often need to access applications remotely that can't be brought onto a workstation or laptop. Given the aura of security thin clients seem to have, it was a shock to many to learn of a serious security flaw in a Citrix client. Affecting all versions from 9.x and below, the flaw stems from ICA through a proxy server and if exploited can result in system compromise.
You can read the official Citrix response at their site. Even “dumb” systems can be the target of malicious hands, sadly enough. They haven't mentioned any servers or workstations becoming compromised through this flaw, though, which is a good thing. Version 10 is not affected.