Washington--The Computer Emergency Response Team warned businesses that a computer virus - dubbed the ``Code Red'' worm - is expected to begin spreading across computer networks on Tuesday night. The virus, which slows Internet speeds and in some cases brings networks down altogether, is targeted at e-mail and electronic commerce applications. It first appeared July 19 and has infected more than 250,000 systems. Microsoft Corp. is distributing a patch for the virus on its Web site, but many companies have not downloaded it. The worm disrupts Web sites by replacing pages with the words ``Hacked by Chinese.'' Computers using Windows NT and Windows 2000 operating systems are affected.