Another source told IDG News Service on Thursday that a portion of the service that redirects third-party-owned URLs (uniform resource locators) to Google Sites or the Google Blogspot service also was affected for about an hour by the DOS attack.

"We are aware that a handful of non-Google sites were impacted by a DoS attack yesterday, and are in contact with some affected companies to help investigate this attack. Google systems prevented substantive impact to our services," a Google spokesman said Friday via e-mail.

Twitter didn't immediately respond to a request for comment.

LiveJournal declined to comment.