Hackers have tried to infect users' PCs with malware by pretending World War III had broken out.

A weekend spam run tried to dupe recipients into downloading the infamous "Storm Trojan" by attaching files that posed as videos of a missile strike by the US against Iran.

The email arrives with provocative subject lines that include "Missle [sic] Strike: The USA kills more then [sic] 20000 Iranian citizens," "USA Declares War on Iran," and "USA Just Have Started World War III," include attached executable files such as video.exe and readme.exe, said Symantec.

"The underlying threats are actually nothing new," said Symantec researcher John McDonald on the company's security response team's blog. "They are simply minor variants of Trojan.Peacomm and W32.Mixor, which have been repacked in an attempt to avoid existing detection and appear to have been largely successful at that." Symantec added that the executable attached to the war-scare spam is actually a worm that downloads and install both Trojan horses.

According to data from MessageLabs, Peacomm - also known as Zhelatin - was the most prevalent piece of malware in the past 24 hours. It accounted for 32 percent of all malicious code being distributed worldwide, said MessageLabs.

By early today, other security companies, including F-Secure, Fortinet, Kaspersky and Sophos, had released signatures to detect the tweaked threat.

Peacomm, which also goes by the nickname "Storm Trojan," is notable because an outbreak in January and February claimed the prize of the biggest malware assault since mid-2005.

Previous spam runs of the malware have enticed users with romantic subject headings around Valentine's Day; the malicious code has been spread through blogs and instant messaging as well as email.