Computer hackers vying in a global contest on Sunday defaced a slew of Web sites, but the damage was confined to the Internet's backwater of small, unsecured sites, security officials said.

The "Defacer's Challenge" got off to a quick start on Sunday with 300 attacks reported minutes after the 2 a.m. EDT official start, said Roberto Preatoni, founder of Estonia-based Zone-H.org, a site that tracks hack attacks.