WASHINGTON -- The email terrified the young mother. "What if I told you I had pics of you?" the anonymous writer asked. "Like a lot. Would you send me more?"

"They were pretty x-rated," he added.

To prove he wasn't bluffing, the mysterious emailer sent four naked or suggestive photographs of the woman, which had been stored in a laptop computer stolen in a recent burglary of her New Hampshire apartment. He threatened to publish them if she didn't send him more explicit ones.

And if she had any doubt that he was a cruel, "sick" person, "then im going to act like one," he wrote.

The harassing emails were emblematic of what U.S. law enforcement officials say is a growing and particularly invasive form of cyberstalking that's getting their increasing attention. It has been given a chilling moniker: "sextortion."

"This is a growing problem," said Wesley Hsu, the chief of the cyber and intellectual property crimes unit at the U.S. attorney's office in Los Angeles, which has handled several such prosecutions. The victims "suffer understandable emotional distress at the moment it happens, and the Internet is unfortunately quite permanent and it can have an effect on these mostly young women for a long time."

"They can perceive it as their life being over," he said.

The crime exacted a lasting psychological toll on the New Hampshire mother, despite a quick arrest. She was devastated by the threat to post her naked photos on the Internet and to mail them to others in her hometown. Almost two years after the stalking ended, prosecutors wrote, she remained "thoroughly traumatized."

On July 10, the 24-year-old woman died in what police in Dover, N.H., called an apparent suicide by hanging. She left behind a 4-year-old son. Bloomberg News is withholding the victim's identity out of respect for the son's privacy and because she wasn't named in court papers.

In an interview several weeks before the suicide, Justice Department prosecutor Mona Sedky said that for the woman, "it was really no different than someone being present with a weapon and trying to make her take her clothes off."

Sextortionists ply their trade not only by stealing equipment but also by hacking into computers, social media accounts and emails, and even hijacking webcams. After obtaining the photographs, they use them to demand ransom in the form of cash or more explicit pictures and videos.

Since 2008, federal prosecutors have charged at least 20 men with this form of extortion in crimes involving hundreds, if not thousands, of victims, according to court papers. They say the crime is vastly underreported.

"Victims of sextortion have disincentives to reporting," said Hsu, the Los Angeles-based prosecutor. "Many are threatened with worse consequences if they go to law enforcement, and they feel deeply embarrassed and ashamed."

The offenders range from teenagers to members of church choirs and teachers. In one case, a Danish man posed as a young boy to obtain photos of an 11-year-old girl in Missouri.

The victims are usually young women and youths, but men have also been targeted. In 2010, a professional poker player's naked photos were emailed to 100 people after he refused to comply with a hacker's demand for $100,000.

Because of the Internet, sextortionists can rack up large numbers of victims. A 28-year-old California man, Karen "Gary" Kazaryan, broke into more than 350 social media, email and Skype accounts to obtain naked photographs -- federal agents discovered at least 1,100 photos of naked or semi-naked women on his computer.

If the victims didn't comply by sending him more photos or videos, he carried out his threat to post them online, "causing horrified victims to receive calls from other friends about how their entire friend network could now see them naked," prosecutors wrote. Kazaryan was sentenced in December to five years in federal prison.

Richard Finkbiner tricked boys and girls into engaging in sexual activity in front of a web camera while he secretly recorded the sessions. Afterward, the 42-year-old Indiana man threatened to publish the videos on pornographic websites unless the victims became his "cam slaves" by engaging in more such activity, according to prosecutors.

When a 17-year-old Cincinnati girl told Finkbiner she had tried to kill herself the previous night after he had successfully coerced her into engaging in sexual acts on video, Finkbiner showed no compassion. "Glad i could help," he wrote.

Finkbiner, who was sentenced to 40 years in prison in 2012, ended up collecting tens of thousands of images depicting the sexual abuse of his victims, prosecutors said.

Other hackers have used software that infected computers with viruses to obtain compromising photos and videos.

A victim of such a hack was Cassidy Wolf, who was Miss Teen California last year when she received an email containing two photographs of her naked in her own bedroom. They had been taken by her laptop's webcam, which had been surreptitiously commandeered by a hacker and used to spy on her.

The email threatened to make the photos and others public if she didn't reply with higher-quality photos and videos, or "do what I tell you to do for 5 minutes" during an online video chat.

"Your dream of being a model will be transformed into a porn star," the email promised. When Wolf didn't comply, the emailer posted the photos on social media sites. He also replaced her Twitter avatar with a half-nude photograph.

"I don't even know how to describe how I felt at the time," the 20-year-old Wolf, who won the most recent Miss Teen USA contest, said in a telephone interview. "I felt violated. It was a modern version of a peeping tom."

It took authorities six months to arrest and charge the extortionist: Jared James Abrahams, 20, a former high school classmate of Wolf's.

Abrahams was sentenced in March to 18 months in federal prison for hacking into as many as 150 online accounts and extorting teenage girls and young women into sending him nude photos and videos. At least two complied with the demands.

Like Wolf, the New Hampshire mother would learn that she knew her anonymous stalker. The suspect was John B. Villegas, a Navy sailor, who was the husband of her son's babysitter.

He was arrested by the Secret Service within a week of sending the first email in July 2012. In March, he was sentenced to 33 months in federal prison after having pleaded guilty to one count of cyberstalking. He also pleaded guilty in state court to stealing the woman's laptop.

Calling Villegas "a sexual cyber predator," federal prosecutors wrote in court papers that the Maine resident was "strikingly callous" -- stepping up his threats even after the mother pleaded that posting the photos would wreck her reputation and endanger her toddler's safety.

"The emotional distress he caused" the mother, prosecutors wrote, "will be everlasting."

A section on 08/03/2014