Thursday night began like any other on "The Late Show With David Letterman," with the host cracking jokes about lying, philandering politicians in his monologue. But then, Letterman did something he's rarely done in his nearly 30-year late-night career: He talked seriously about his personal life.

Letterman revealed that he was the victim of a recent $2 million extortion attempt by a man who threatened to write a screenplay about the talk-show icon having affairs with employees. Letterman admitted to having the affairs and said that he'd helped police arrest the man, later revealed to be a CBS employee who works for the show "48 Hours."

"I have a little story that I'd like to tell you," Letterman began. "This morning, I did something I've never done in my life. I had to go downtown to testify before the grand jury ... [and] tell them all of the creepy things that I've done."

Letterman, 62, went on to explain that he found a package in his car three weeks ago from someone claiming to have information about the affairs who later demanded $2 million to keep them secret.

"I know that you do some terrible, terrible things, and I can prove that you do these terrible things," he said the note warned. "Sure enough, contained in the package was stuff to prove that I do terrible things."

Letterman began dating wife Regina Lasko in 1986. They married this March and have a 6-year-old son, Harry. It was not revealed when the affairs with staffers took place.

When the unnamed extortionist confronted Letterman, the talk-show host said he went to the Manhattan district attorney's office, where an investigation was launched, resulting in an arrest on Thursday afternoon.

CBS released a statement confirming the investigation. "CBS was made aware of an ongoing police investigation involving David Letterman and an employee at '48 Hours,' who was subsequently arrested ... on charges of attempted grand larceny in the first degree. ... CBS is cooperating fully with the authorities, and the employee has been suspended pending the results of the investigation."

Describing his grand jury testimony, Letterman somehow found a way to milk laughs from a serious situation, much as he did in 2000 when he returned from emergency heart surgery.

"The creepy stuff was that I have had sex with women who work for me on this show," Letterman told the audience, who appeared unsure if the story was a joke or the real deal and greeted the revelation with a mixture of laughs and confused gasps. "My response to that is, yes, I have. I have had sex with women who work on this show. Would it be embarrassing if it were made public? Perhaps it would, especially for the women." That line brought a big laugh from the audience, with Letterman pretending to be nonplussed by their reaction.

"I feel like I need to protect these people -- I need to certainly protect my family," said Letterman, who has hosted the "Late Show" on CBS since 1993. "I need to protect myself ... hope to protect my job."

Prior to the arrest, Letterman said he handed over a phony $2 million check to the alleged extortionist. The Manhattan district attorney's office is expected to hold a press conference on Friday, when more details about the alleged plot will be revealed. For now, Letterman -- who was the subject of a failed 2005 kidnapping plot to hold son Harry for $5 million ransom -- said he prefers not to discuss it anymore.