Cybercriminals are spreading a malicious Trojan horse <A HREF="http://news.zdnet.com/2100-1009_22-5898272.html?tag=zdnn.alert">under the guise of an update to Skype.</A> The Trojan horse, a variant of IRCbot, arrives in an e-mail purporting to be an update to Skype, the popular Internet telephony application. Once opened the malicious software displays a phony installation error message. It then blocks access to security updates and installs a back door on computers.