Security experts today warned of a newly discovered mutant version of the IRCbot (aka Fanbot) Trojan, which is being distributed via email disguised as the latest release of the popular Skype VoIP software client.

MessageLabs said that it has intercepted more than 800 copies of the mutant Trojan, which purports to be version 1.4 of Skype's client software released last week.

When executed the malware displays a fake 'installation error' box while installing itself as '%sysdir%\remote.exe', altering the registry and shutting down shared access and Windows update services.

It then tries, but fails, to connect to either an IRC server named 'jojogirl.3322.org' (channel name #Phantom) or 'smallphantom.meibu.com'.

"This latest 'spear' phishing attack, where Skype users are being targeted with an email that appears to come from Skype, is the first case we've seen that specifically mentions Skype," said Maksym Schipka, a senior antivirus researcher at MessageLabs.

"It is another clear example of how malware writers are quickly exploiting newly identified security holes, as we saw with the Zotob attack, and now with releases of popular software applications in order to try and spread their malicious payloads."

The Trojan typically arrives in an email with the following subject line:

'Hello. We're Skype and we've got something we would like to share with...; Share Skype.; Skype for Windows 1.4; Skype for Windows 1.4 - Have you got the new Skype?; What is Skype?'

The body text of the bogus email is as follows:

Dear user,
Skype is a little piece of software that lets you talk over the Internet to anyone, anywhere for free. And it just got even better -- download the latest version of Skype: Our call quality is the best ever for talking, laughing and sharing stories. You can forward calls on to mobiles, landlines and other Skype Names. Make calls instantly from Outlook email or Internet Explorer with our new toolbars. Personalise your Skype -- play around with sounds, ringtones and pictures to show the world who you are.
For further details see the attached document.
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