Representative Anthony D. Weiner, one of the most prolific users of social media among politicians, said his Twitter account was hacked this weekend when someone sent out a lewd photograph under his name to a young woman in Seattle.

The episode unfolded Saturday night when it was reported on the Web site biggovernment.com, run by the conservative blogger Andrew Breitbart. It played out all day Sunday on the Internet, with Mr. Weiner, a Democrat who represents part of Brooklyn and Queens, addressing the matter on his own Twitter and Facebook accounts, and with bloggers from the left and the right arguing about whether this might be the start of a scandal or an example of how easy it is for political rivals to harm each other’s reputations using new technologies.

Neither Mr. Weiner, an outspoken defender of liberal positions, nor Mr. Breitbart returned messages requesting comment on Sunday night.

“Anthony’s accounts were obviously hacked,” Dave Arnold, a spokesman for Mr. Weiner, told The Associated Press. “He doesn’t know the person named by the hacker, and we will be consulting on what steps to take next.”