Alureon (or TDSS) is a trojan designed to steal data by intercepting a systems network traffic and searching it for usernames passwords and credit card data. PCs usually get infected by manually downloading and installing software. Alureon has been bundled with rogue software like Security Essentials 2010.
It can manipulate the Windows registry and block access to Task Manager and the desktop. It also blocks access to Windows update, and disable some antivirus programs.