Yet more variants of the mass-mail Sober worm are making the rounds of the Net and could infect Windows-based computers, antivirus firms warned Tuesday. Thus far, the variants present a low risk and haven't been widely distributed.
Both Kaspersky Lab and Symantec have detected worm variants. Kaspersky noted three variants of E-mail-Worm.Win32.Sober, which Symantec identified as W32.Sober.S@mm.
The variants are modifications of the same program, said Kaspersky, which is based in Moscow. A "large number of samples" of the variants have been intercepted in e-mail traffic, indicating that the worms are spreading by spam containing infected messages, Kaspersky said in a statement. The variants arrive as an attachment to infected messages.
The messages might not have a subject line or text, but can be identified by the attachment name. The attachment names thus far identified are: Exceltab-packed_list.exe; Liste.zip; Reg-List-Dat_Packer2.exe; reg_text.zip; Word-Text.zip; Word-Text_packedList.exe; Word-Text_packedList.zip.
The worm activates only if a computer user clicks on the attachment, which causes a false error message, "WinZip Self-Extractor. WinZip_Data_Module is missing ~Error," to pop up, Kaspersky said. The worm variants copy themselves to the Windows system directory and then registers the files to the system registry so that the worm launches every time Windows is rebooted.
The worm uses its own SMTP (Simple Mail Transfer Protocol) engine to spread, Symantec said. Spam that it generates is in either English or German, said Symantec, which is based in Cupertino, California. Mass mailing of spam containing the worm could clog mail servers or degrade network performance, the company said. Instructions for removing the worm from infected systems can be found at Symantec's Web site, http://www.symantec.com, by clicking on the Sober variant listing under "latest threats."
As always, the antivirus companies advise that computer users exercise caution in opening attachments.