The heart of the Internet sustained its largest and most sophisticated attack ever, starting late Monday, according to officials at key online backbone organizations.

Around 5:00 p.m. EDT on Monday 21 October 2002, a "distributed denial of service" (DDOS) attack struck the 13 "root servers" that provide the primary roadmap for almost all Internet communications. Despite the scale of the attack, which lasted about an hour, Internet users worldwide were largely unaffected, experts said.

FBI officials would not speculate on who might have planned or carried out the attack.

"This was the largest and most complex DDOS attack ever against the root server system," said a source at one of the organizations responsible for operating the root servers.

Ordinary Internet users experienced no slowdowns or outages because of safeguards built into the Internet's architecture. A longer, more extensive attack could have seriously damaged worldwide electronic communications, the source said.