Companies cleaned up their computer systems on Sunday after a fast-spreading worm shut down Web servers in an attack that slowed the Internet for users around the world. South Korea, the world’s most wired country, was believed to be hit the hardest in the attack, which began early Saturday, spreading through network connections rather than e-mail as many viruses do. The worm, dubbed “SQL Slammer” (“sequel”) because it exploits a weakness in Microsoft Corp.’s Windows 2000 (news – web sites) SQL server database software, did not delete or otherwise touch data. However, it crashed servers and congested traffic on the global network for a few hours, slowing downloads by as much as 50 percent, according to Internet performance monitoring firm Keynote Systems. Full Story