The fast-spreading ``Code Red'' Internet worm, which disrupted U.S. government Web sites last week, is likely to start multiplying again on Tuesday and could slow down the Internet, officials said on Monday.

Code Red, which first surfaced on July 19, could slow down the Internet worldwide if it re-emerges as expected at 8 p.m. EDT Tuesday, according to the FBI's National Infrastructure Protection Center (NIPC) and other online security watchers. Computers running the Windows NT or Windows 2000 operating systems and Microsoft's (MSFT.O) Internet Information Server (IIS) software version 4.0 or 5.0 are vulnerable to infection and the users should install a software patch. Instructions for the patch are available at www.digitalisland.net/codered. Computer users running Windows 95, Windows 98 or Windows Me are less vulnerable, and no action was recommended for them. The worm, named for a caffeinated soft drink favored by computer programmers, installs itself on server computers that then are instructed to blitz government Web sites and others with data, which can slow them down. The version of Code Red that could re-emerge on Tuesday ''has mutated so that it may be even more dangerous,'' the statement warned. ``This spread has the potential to disrupt business and personal use of the Internet for applications such as electronic commerce, e-mail and entertainment.'' The warning was posted by Microsoft Corp., the FBI center, Carnegie Mellon University's Computer Emergency Response Team (CERT) and other groups.