Almost a year after his teenage daughter's attacker was sentenced in a high-profile sexual assault case, Alexander Prout hoped his family could get back to normal.

But relief from the torment his family experienced after his daughter was assaulted at St. Paul's School in Concord, N.H., and during the trial for convicted attacker Owen Labrie, a former student at the elite prep school, was short lived.

Within days of the conviction, a detective from the Concord police department called to say strangers threatened the family on websites dedicated to outing sexual assault victims, and from other dark corners of the internet.

"It was horrifying to see," said Mr. Prout, whose daughter has since identified herself publicly. "[They had] photos of all of my children, all of our specific personal information, including links to all our social media sites, family photos, photos of our home."

The Prout family may be a high-profile case, but they're hardly alone. Around 18 percent of internet users experience severe online harassment, including physical threats, harassment over a sustained time period, stalking, and sexual harassment, according to a 2014 survey by the Pew Forum.

But US law does not require federal investigators to track instances of online harassment. A bill introduced Sept. 13 by Rep. Katherine Clark (D) of Massachusetts would require the FBI to collect data on cybercrimes against individuals, and include those figures in the Uniform Crime Reports, the agency's annual repository of US crime data, and the National Incident Reporting System.

"If the FBI can provide data on murders and robberies and arson, they should also be able to collect data on the number of cyberstalkings and any other cybercrimes against an individual," Ms. Clark told Passcode.

Her office has also asked Attorney General Loretta Lynch to release data on how many times the Department of Justice prosecutes federal online stalking and abuse cases, which violate current federal law?.

Under the new law, the FBI would add "cybercrimes against individuals" – online stalking, harassment, and threats – to its main crime reporting systems. The attorney general would release an annual summary of the cybercrime data, and the Department of Justice would have to come up with a national strategy for reducing these online crimes.

The legislation may seem like a small step when measured against the kind of harassment the Prouts experienced. But proponents like Mary Anne Franks, the legislative and tech policy director at the Cyber Civil Rights Initiative, hope that more data will help lawmakers, law enforcement and advocates make smarter decisions about how to fight digital harassment.

"Having a better sense of the prevalence and incidence of these crimes would help us, first, to understand their nature and dynamics," Ms. Franks said via email. "Requiring reports also forces agencies to be more transparent about their policies and can push them to improve them."

A 2006 survey by the Department of Justice found that 3.4 million Americans experienced stalking or harassment, a quarter of whom (850,000) were stalked or somehow harassed online. But that data precedes the rise of smartphones and social media — technologies that have made the internet ubiquitous, for better and for worse. A 2014 survey by the Pew Forum shows that some 40 percent of internet users experience harassment online, with 18 percent experiencing "severe" abuse like threats or prolonged stalking.

The problem has become a major topic of public debate in recent years. Despite widespread attention, however, the public still doesn’t know how often online harassment turns criminal – or how often it’s prosecuted when it does.

Clark has already introduced several bills the congresswoman meant to tackle online harassment, which has become one of her signature issues. She first got involved with the issue in October 2014, when one of her constituents, Boston-based video game developer Brianna Wu, had to temporarily flee her home along with her family because of extreme online threats.

In November 2015, Clark proposed the Interstate Swatting Hoax Act, a piece of legislation that would make it a federal offense for anonymous web users to call police and falsely report that a violent incident was in progress. Heavily armed officers typically respond to the address to find little more than terrified victims. Three months after proposing the bill, Clark herself was swatted.

"It's important to use my position as a member of Congress to try to extend the protections that I have with this office to everyone," Clark told Passcode in April.

Last week, Clark also sent an open letter to Attorney General Lynch asking for data on how often the Justice Department has prosecuted online stalking and harassment over the past five years. Her office has been asking for the data for 22 months, Clark said, with little progress.

"We have had meetings. We call every few weeks. We've written letters. And we just have been stonewalled," the congresswoman said.

The Justice Department prosecuted just 10 cyberstalking cases between 2009 and 2012, according to Danielle Citron, a professor of law at the University of Maryland who studies online harassment. In 2015 and 2016, Clark introduced language in reports attached to Department of Justice appropriations bills that urged it to prioritize these crimes. She hopes that having data on prosecutions will show whether Justice Department officials heeded those instructions.

More numbers would also help lawmakers and advocates know where to direct their energies in the fight against online harassment, according to Ms. Citron.

"Publicly released statistics would allow the public to engage in a dialogue about [the] law's enforcement and whether further training and resources are needed," Citron said in an email. "Mandatory training and reporting would encourage the enforcement of existing law, which is desperately needed."