Comcast's online services were offline for several hours last night for thousands of East Coast customers.

The outage was mostly in the greater Boston and Washington, D.C., areas, including Baltimore, according to corporate spokesman Charlie Douglas.

Philadelphia was not affected, and nowhere was phone or television service disrupted, he said.

Users started failing to get on the Internet about 8 p.m., and the system was back up and running about 11 p.m.

"If anyone is having any residual issues, they just need to restart their modems," Douglas said. "That should take care of it."

The outage was caused by unidentified problems at two of Comcast's major computer operations centers, in Framingham, Mass., and Manassas, Va., he said.

The trouble apparently had to do with domain name servers, which translate Web addresses (such as www.philly.com) into numerical strings called IP addresses.

Such problems can be side-stepped, by using alternatives such as OpenDNS and Google Public DNS, writes the Washington Post's Rob Pegoraro on his "Faster Forward" blog.

Comcast says it is the leading provider of high-speed Internet services to American homes, with more than 16.7 million subscribers.

How many were affected by last night's outages was unclear, Douglas said.