The attachment purports to be a recording of a call involving the recipient of the e-mail but it downloads the Troj/Dorf-AH and malicious software from a dangerous website when it is opened.

It then tries to persuade the victim to buy fake security software, online security firm Sophos said.

A spokesman added:

"It may seem hard to believe that anyone would fall for a trick like this, but it wouldn't be a surprise if people tried to run the attachment just out of curiosity as to what it contained.

"Some may even assume it is a joke recording and not realise they are putting their computer, and indeed their wallet, in danger."