The authorities concerned have warned computer users on Thursday that a destructive worm named Nyxem normally activates on the third day of every month and attacks Microsoft Windows operating system.

The Computer Emergency Response Team (CERT-In), working under DIT dubbed the worm as very destructive. The worm is also called as Blackmal, Kapser and MyWife. It is reported to propagate by sending an e-mail attachment to target users. It is meant to spreads through network shares.

According to the warning, it is observed that upon activation it replaces the content of user's files and reduces the size of all user data files to 1KB. When a user clicks on the attachment, the worm gets executed. It opens a .ZIP archive with the same name in the Windows system folder to hide its functionality.

Next, it copies itself to the system folder with the filenames: scanregw.exe, Winzip.exe, Update. exe, movies. exe, Zipped Files.exe. The most dangerous aspect is that it deletes the files related to anti-virus applications.

The worm attempts to spread to network shares with weak passwords. The emails sent by the worm use some obscene subject lines message content and attachments. Mostly this contains obscene language titles as per the govt. information.

To protect from the worm attack, CERT-In has advised the users not to open suspicious e-mails or mails with some funny subject/attachment.