Troj_Nurech.AJ is a Trojan that arrives as a downloaded file from malicious Web sites by other malware. It can also arrive bundled with malware packages as a malware component. It can be installed manually by a user.

It disables Classic Start Menu on systems running on Windows NT, 2000, XP, and Server 2003. It also hides the path address, shows hidden system files, and hides file extensions as part of its malicious routine.

It downloads encrypted files from certain URLs. As a result, routines of the downloaded files are also exhibited on the system.

Technical details can be found at this Trend Micro page.