Stop us if you've heard this before. There's a new viral menace on the Net which attempts to con PayPal users into handing over credit card details. Mimail-J, the latest in a series of security-threatening worms, has spread quickly since its first appearance yesterday.

Mimail-J typically arrives in an email with a subject line of "IMPORTANT" and an attachment named either www.paypal.com.pif or infoupdate.exe.

Except for some changes in the text of the infected email the worm's code is almost exactly the same as Mimail-I.

Again, targets of the scam are advised to run an attached program, which (surprise, surprise) contains viral code.

If you run the program, a dialog box pops up requesting you to enter a range of information about your credit card. This includes your full credit card number, your PIN, the expiry date. The dialog includes a PayPal logo in a further attempt to appear legitimate, as shown by F-Secure here.

As well as attempting to filch financial information, Mimail-J sends itself to everybody whose email addresses appear on a user's hard disk.

As usual, Mimail-J infects only Windows machines.

Since its appearance yesterday, Mimail-J has spread rapidly. Email filtering firm MessageLabs has blocked approximately 23,000 copies of Mimail-J to date. It's the second most common viral nuisance on the Net today, according to MessageLabs' statistics.

Alex Shipp, senior antivirus technologist at MessageLabs, described Mimail-J as a "medium risk" threat.

Because the characteristics of viral emails sent from infected machines differ from the pure version of the virus, Shipp has been able to look at how the viral author behind Mimail-J attempted to kick-start the infection process. The original seed virus contained an infectious attachment called infoupdate.exe compared to the www.paypal.com.pif infector associated with secondary infections.

This factor has allowed Shipp to conclude that the author of Mimail-J seeded the infection using spamming software (ratware).

Five variants of Mimail, including one that launches a DDoS attack against anti-spam sites from infected PCs, are listed in MessageLabs' daily top ten most unwanted list.

Standard defence precautions against viral attacks from all variants of the worm apply: users should update their AV signature definition files to detect the virus and resist the temptation to open suspicious looking emails. Users should also remember that email security checks from financial institutions are almost certainly bogus and should be ignored. ®

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