Hackers have spammed out a widespread attack to unsuspecting computer users, disguised as an electronic greeting card.

The email messages, which Sophos is seeing in large numbers in its global network of spamtraps, have the subject line "You have received an eCard" and contain the following message body:

Good day. You have received an eCard

To pick up your eCard, open attached file

We hope you enjoy you eCard.

Thank You!

Careful Internet users should notice that the email messages are not personalized with the recipient's name, and they give no hint as to who might have sent the electronic greeting.

Attached to the email is a file called ecard.zip, which contains a malicious Trojan horse that Sophos proactively detects as Mal/WaledPak-A. Users of other antivirus products may need to check that their security software is updated.

Of course, it's never a good idea to open unsolicited email attachments on your PC. But the fact that hackers still persist in schemes such as this one suggest it continues to be an effective way for them to build botnets, steal identities, and con unsuspecting users out of their money.

Graham Cluley is senior technology consultant at Sophos, and has been working in the computer security field since the early 1990s. When he's not updating his other blog on the Sophos website you can find him on Twitter at @gcluley. Special to Dark Reading.