Trojans are malicious applications that pose themselves as legitimate software in order to trick users to install them. Once on the victim's machine, it may run any number of malicious process to steal vital information or inflict damage to other software.
"A vulnerability exists in the XMLHTTP ActiveX control within Microsoft XML Core Services that could allow for remote code execution. An attacker could exploit the vulnerability by constructing a specially crafted Web page that could potentially allow remote code execution if a user visited that page or clicked a link in an e-mail message. An attacker who successfully exploited this vulnerability could take complete control of an affected system. However, user interaction is required to exploit this vulnerability." Microsoft Product Security
Original Article can be found at: http://www.microsoft.com/technet/security/bulletin/ms06-071.mspx