The Storm malware, which first appeared in January of this year, is showing no signs of slowing down - just this week reinventing itself as a website membership confirmation message.

Storm, like many Trojans, is designed to infect as many end-user systems as possible and add them to botnets that can be used to attack other sites, relay spam or for other purposes.

The malware is particularly resilient and pervasive, having started off life attached to junk emails bearing provocative news headlines, later moving on to fake greeting cards notifications and advertisements for salacious photographs.

Previous campaigns have lasted for weeks at a time, but the latest Storm-related generations of spam are changing more quickly than ever.

"Spammers are modifying or launching new spam campaigns almost daily," said Bradley Anstis, director of product management at security firm Marshal, in a statement.

The latest junk emails typically pose as confirmation messages for an account that the user has supposedly already created on a website such as "CoolPics," "Joke-A-Day," "Web Players" or more than a dozen other names, according to security organisation the SANS Institute.

The emails ask the user to log into the site in question - represented by a numeric IP address - to change their temporary login details.

When accessed, the site attempts to load malicious code onto the user's system via a WinAmp exploit as well as asking the user to download the Storm Trojan under the name "applet.exe" - supposedly a "Secure Login Applet," according to SANS.

Security vendors are updating their programs to recognise and block this latest Storm scam, according to SANS. "That may actually be useful until the next version is released in a couple days," said Johannes Ullrich, a handler at SANS' Internet Storm Center, in an advisory.

The binary itself changes every 30 minutes or so, according to Ullrich.

"These criminals are clever and highly adaptive," said Marshal's Anstis. "This is simply their latest attempt to fool unsuspecting email users into infecting themselves."

Ironically, the sheer prevalence of Storm may mean that current spam bombardments are "a lost cause," according to SANS' Ullrich.

"People are either (already) infected or they know how to protect themselves," he wrote.