Yahoo Inc. (YHOO), the most-used Internet site, has shut down all its user-created Internet chat rooms amid concerns that adults were using the sites to try to have sex with minors.

The giant Internet media company closed down those chat rooms and the ability to create new ones "in the past week," said Yahoo spokeswoman Mary Osako.

Chat rooms created and sponsored by Yahoo itself remain open, Osako said. The number of user-created chat rooms is variable at any given time and Yahoo does not track that figure, she said.

The user-created chat rooms in question, where Internet users converse in real time, had names including "Girls 13 And Under For Older Guys" and "Girls 13And Up For Much Older Men" and were all listed under "education chat rooms," Houston television station KPRC (search) reported.

"We are working on improvements to the service to enhance users' experience and their compliance with our terms of service," Osako said. "Yahoo condemns theuse of Internet tools for illegal activities."

KPRC reported last month that major advertisers including PepsiCo Inc. (PEP), Georgia-Pacific Corp. (GP) and State Farm Mutual Automobile Insurance Co. removed their ads after the station found the ads were appearing on Yahoo user-created chat rooms that were aimed at sex with children.

"As soon as we found out we pulled our ads," said Pepsi spokesman Dave DeCecco. "We were totally unaware our ads were associated with those chat rooms -- and that was back in April."

Pepsi continues to advertise on other parts of Yahoo's site, mostly in sports and music sections, but pulled all its ads in user-created chat rooms.

"They were down the same day we found out about it," DeCecco said, referringto the ads on user chat rooms.

"We were horrified to find out we were on those sites," said Georgia-Pacificspokeswoman Robin Keegan. "As soon as we found out, that day we pulled that advertising."

A spokesperson for State Farm was not immediately available to comment.

The concern over online safety for children using the Internet has surged with the number of people using the Internet, which allows for anonymous and sometimes hard-to-trace communication and content.

It's also not the first time that Yahoo has faced the issue of users taking advantage of its free services to lure young children.

A minor and his parents in May filed a $10 million lawsuit against Yahoo anda man who once operated a Yahoo Groups site where members traded child pornography.

Many attorneys argue that the Communications Decency Act (search) shields Web sites from responsibility for material posted by users.

But the lawsuit, filed on May 9 in U.S. District Court for the Eastern District of Texas, charged that Yahoo breached its duties by allowing co-defendant Mark Bates and others to share child pornography on a site, called Candyman, that Bates created and moderated via the Yahoo Groups service.

A child pornography investigation led by the Federal Bureau of Investigation (search) and dubbed Operation Candyman targeted Yahoo Groups users and ultimately resulted in the arrest of more than 100 people in the United States.