A tricky malicious program has become more prevalent in spam, but experts don\u2019t know what its creators plan to do with it.Many vendors are rating the malware\u2014called "Warezov," "Stration" and "Stratio"\u2014as a low risk. But they also say it is tricky to deal with.The malware is a mass-mailing worm that affects machines running Microsoft\u2019s Windows OS. When the malware infects a computer\u2014usually after the user has opened an attachment containing the worm in a spam e-mail\u2014it sends itself out again to other e-mail addresses found on the computer. The code is then capable of downloading new versions of itself as frequently as every 30 minutes from a batch of websites, said Mikko Hypponen, chief research officer at F-Secure, a security company in Helsinki.Those new versions are created by a program on a server controlled by the hacker, Hypponen said. In the past, malware has been known to create variations of itself, but the code to create those variations was contained inside the malware. So when a sample was obtained, security analysts could study it and identify potential new versions, he said.Now, the hacker\u2019s program is compiling the code and rapidly churning out new versions, but analysts don\u2019t know how the new code is generated.That characteristic is a headache for security software firms that issue special updates to their software to detect the malware. F-Secure alone has issued at least 150 signatures for the malware."It gets very complex to detect an attack like that because the code keeps changing," Hypponen said.Security firm Sophos has detected some 300 versions of the malware. For October, the malware was one of the most common pieces of malicious code found in spam messages, said Carole Theriault, senior security consultant with Sophos.Since infected computers look to other domains to receive updated code, F-Secure has worked with ISPs to shut down domains hosting the new variants. So far, nine of 10 domains have been shut down, Hypponen said.Oddly, the malware doesn\u2019t appear to do anything yet on the victims\u2019 computers. It\u2019s estimated up to a few hundred thousand computers are infected, a sizable number, but not quite on the scale of large malware problems from a few years ago, Hypponen said.A hacker could be waiting to harness enough infected computers to start a denial-of-service attack or send spam or rent out the network to a spammer, Hypponen said."We hope to one day find out why they are doing this," Hypponen said. "We hope it\u2019s nothing too bad."-Jeremy Kirk, IDG News Service (London Bureau)Related Links:\n\nCeleb Sites New Best Way to Pick Up Malware\n\nHackers\u2019 Project Hides Browser-Busting Code\n\nSophos Antivirus Blocks Unwanted ProgramsCheck out our CIO News Alerts and Tech Informer pages for more updated news coverage.