The e-mail contains a link to the 'greeting', which is actually an executable file that downloads a Trojan horse virus.

Security firm Sophos says that because the e-mail does not arrive with an attachment, people may wrongly think it is harmless.

However, it says more cyber criminals are using a combination of e-mail and the Internet to infect computers.

A spokesman said:

"Companies need to defend their workers with a comprehensive web gateway security as well as protecting their desktops and servers."