A federal judge ordered Microsoft Corp. to stop bundling its Internet software with its widely used Windows computer operating systems, dealing at least a temporary blow to the software giant's plans to dominate one of the computer industry's hotly contested markets.

Judge Thomas Penfield Jackson's order bars Microsoft from requiring personal-computer makers that license its operating system to also accept its Web software. The ruling, a victory for the Justice Department, applies not just to the Windows 95 operating system...