New Delhi: Computer users are likely to fall prey to an infectious Trojan horse as it disguises as a Microsoft security update. Hackers have been sending security update e-mails to various computer users' hours before the genuine update dispatch time on Tuesday.

The security firm Sophos confirmed that the e-mails with the subject line 'Security Update for OS Microsoft Windows' claimed to have come from Steve Lipner at securityassurance@microsoft.com

The e-mail asserts the innocent users that the attached file is a high-priority update and needs to be installed by users of various versions of Microsoft Windows. However downloading the attached file will infect Windows computer users with the Mal/EncPk-CZ Trojan horse, and could give hackers control over the PC. The file attached to the file is named KBxxxxxx.exe (where 'xxxxxx' is a randomly generated number) in order to disguise itself as a knowledge-base file.