BALTIMORE -- It may have happened to you. It begins with one of those annoying pop up ads for a porn site and ends with unexplained charges on thousands of phone bills.

WBAL-TV reported that pop up ads are as unavoidable as they are annoying. Click the 'X' in the corner and they disappear. But out of sight doesn't always mean gone.

"There are tens of thousands of consumers who have been billed without their authorization," said Federal Trade Commission attorney Jim Cohm.

The Federal Trade Commission has received thousands of complaints from Internet users who have discovered that a pop-up ad from a company called Alyon Technologies in Lakewood, N.J., has secretly dialed them into porn sites -- porn sites they had no intention of visiting and porn sites charging $4.99 a minute.

A pop-up ad from Alyon interrupted Natalie Furth, of Annapolis, Md., in the middle of an e-mail she was writing. It was clearly advertising porn. "They were mostly movies -- very, very specific and very graphic," she said.

Natalie says she immediately clicked the 'X' in the corner to get rid of it. But she still got billed by Alyon at "$73.35 at $4.99 a minute."

A bill she refuses to pay.

"I think they should be put out of business," said Furth. "If not, put in jail because it is complete fraud."

A public relations firm representing Alyon says not all online billing systems are 100 percent accurate, saying in part, "Nobody bats a thousand. We have a 1 to 1½ percent margin of error. We are a legitimate organization and are not out to gouge anyone."

Can this scenario be explained away as accidental?

"It would be highly unlikely that tens of thousands of consumers would be billed without their authorization in an accidental sense," said Cohm.

It happened to Marcus Harriday, 14, as well. After finishing his homework, Marcus is allowed to play games on the Internet.

"I went on Cartoon Network and I played the games. I switched and went to Nickelodeon and then when I went to Nickelodeon, the ad popped up," he said.

"Did you see anything on the ad?" asked Collins. "No, there was no picture all they had was writing," Harriday said. "It gave you a choice yes or no. I pressed yes, because I thought it was a game for Nickelodeon." The ad disappeared. What Marcus didn't know as he continued to navigate the Nickelodeon site is that Alyon connected him to a $4.99 a minute porn site and then sent the bill to his mom for $638.69.

WBAL asked Marcus' mother about the bill.

"Pamela, it appears this company took advantage of a minor and then charged you for something you clearly weren't interested in. What's your reaction to that?" the reporter said.

"I was totally upset," said Pamela Harriday. "My family just had a nice Christmas and thought I would be debt free and then $600 more that I wasn't expecting."

Pamela wrote Alyon explaining this was a mistake. The company agreed to slash a couple hundred dollars off the bill, but demanded the balance.

"I was afraid of how far they would go," said Pamela.

"It's a gyp on something that shouldn't happen," said Marcus.

Over the summer, the FTC took legal against Alyon. The company must now disclose its sales terms and verify the person they are billing is in fact the user of the service, but apparently that hasn't stopped them.

"Complaints keep coming in to this day," said Cohm.

If the FTC determines Alyon is violating the court order, it could face contempt charges. If you have a complaint against Alyon, you can file a complaint with the Federal Trade Commission online.