Internet security companies said Monday that they discovered a new version of the MyDoom e-mail worm circulating on the Internet.The new version, MyDoom.C, is a modified copy of the virus that ravaged the Internet in January. Unlike its predecessor, however, the new variant does not use e-mail or the Kazaa peer-to-peer network to spread and is not expected to make much of an impact on the Internet, said managed security services provider LURHQ.MyDoom.C both refines and tames the earlier version of the virus, known as MyDoom.A. Among other changes, the new virus fixes problems with the original MyDoom e-mail worm, including errors in the worm's code that made it impossible for many MyDoom-infected machines to launch a programmed denial of service (DoS) attack against The SCO Group's Web site, www.sco.com. Gone also is the expiration date that told machines infected with the original MyDoom virus to stop their DoS attack on Feb.\u00a012, 2004, LURHQ said.Also, instead of depositing a file that opens a backdoor on infected machines, the new virus distributes a compressed archive of the worm's original source code, the company said.However, the MyDoom.C author also removed many of the most dangerous features of the original virus, including the highly efficient SMTP (Simple Mail Transfer Protocol) engine that enabled infected machines to spew out e-mail messages containing the virus. That component made the original MyDoom worm the fastest spreading e-mail worm in history, easily defeating Sobig-F, the previous record holder, according to antivirus software companies, the company said.Instead, MyDoom.C seeks out and infects machines that are already infected with the original MyDoom virus by searching for machines that are listening on port 3127, a telltale sign of MyDoom infection, said security company iDefense in a security alert.That approach will give MyDoom.C a solid base of as many as 500,000 machines, but will keep MyDoom.C from spreading much beyond the community of already-infected machines, LURHQ and iDefense said.The MyDoom.C author also removed a Trojan horse "backdoor," but included a copy of the worm's source code, which is deposited on machines infected with the new variant, the companies said.Unlike the first MyDoom virus, MyDoom.C takes its sights off of The SCO Group Web site, but continues an attack on Microsoft's Web site that was introduced by the MyDoom.B variant, LURHQ and iDefense said.If started on or between Feb. 8, 2004 and Feb. 12, MyDoom.C- infected machines will launch randomly timed DoS attacks against Microsoft.com. Machines started after the Feb. 12 will launch constant attacks against the\u00a0company's Web page, LURHQ said.An analysis of the worm's code also uncovered an IP\u00a0address linked to www.ford.com, the Web page of Ford Motor. However, it is not clear whether the worm targets Ford, iDefense said.The lack of aggressive spreading features, a staple of most e-mail worms, and the inclusion of the MyDoom.A source code may mean that the MyDoom author is closing shop and handing off his creation to other virus writers to refine, LURHQ said.