The vitriol from strangers on Twitter is worst when Kate O’Reilly tweets about politics.

People call her stupid, lob harsh insults and make lewd references to female anatomy. O’Reilly, a longtime Twitter enthusiast from Minneapolis who has more than 5,000 followers, said that she gets harassed by strangers once or twice a month.

“It’s hard to gauge what is appropriate, [when to] let it go and what is a real threat,” she said.

What’s not hard to gauge is the reach of online harassment. From inappropriate name-calling to death threats, cyberbullying is a pervasive and very real problem for adults as well as teens.

“We’ve created a culture online in which harassment is normal and expected,” said Shayla Thiel-Stern, an associate professor at the University of Minnesota who studies social media.

Seventy-three percent of adult Internet users have witnessed online harassment and 40 percent have experienced it, according to the first ever Pew Research report on the topic. While men were more likely to experience some form of harassment, the study — published Wednesday — found women were more likely victims of severe harassment, including sexual harassment and stalking.

The list of examples is long and varied in severity, from personal attacks in online comment threads to leaked celebrity nude pictures to recent death threats against feminist critics of video games.

Cruelty isn’t unique to the Internet, but the anonymity and accessibility it offers feed online attacks.

“It’s much easier for us to be mean online than in a face-to-face situation,” said Justin Patchin, a professor of criminal justice at the University of Wisconsin-Eau Claire, and co-founder of the online Cyberbullying Research Center. “It’s that physical separation [that] creates this ability to say things that some people wouldn’t normally say.”

Half of the adults who have been harassed online do not know the person behind the messages, according to Pew.

Social media platforms were the most common site of online abuse, followed by comments sections of websites, video games and e-mails.

Then there are trolls — those Internet users who purposely seek to harass others.

William McGeveran, a University of Minnesota law professor, has dealt with some of them when blogging about — what else? — online harassment.

“If you do that, you get swarmed and name-called in comment sections,” he said. “To me, it was a little bit like someone hitting you with road rage, cutting you off and giving you the finger on the highway. It’s upsetting and frustrating, but that was as far as it went for me.”

More concerning, he said, are Pew’s finding that 18 percent of Internet users have been subject to more severe harassment. Young women, in particular, find themselves targets. Twenty-six percent of women ages 18 to 24 told Pew they had been stalked online; 25 percent had been the targets of sexual harassment.

“Often people brush off harassment by saying it’s an extreme case and it’s the price we pay for all the great benefits of the Internet,” McGeveran said. “This study suggests that’s wrong.”

Is it criminal?

Despite the fact that Patchin’s Cyberbullying Research Center is focused on teens, he receives more e-mails from adults who are distraught about online harassment and unsure about what to do.

“If you’re a teen being bullied or cyberbullied, you can go to the school. There are disciplinary responses,” he said. “As an adult, you don’t have that.”

Some online harassment can be criminal — for instance, when there is a threat to commit violence. But speech protected by the First Amendment leaves a lot of gray area.

“One of the big problems with enforcement is being able to define, in a usable legal way, what we mean when we talk about online harassment,” said Raleigh Levine, a professor at William Mitchell College of Law who focuses on First Amendment and media law.

Some states, such as California, have enacted laws against “revenge porn,” which allow people who post nude photos or videos online without consent (usually by an ex-spouse, boyfriend or girlfriend) to be prosecuted.

But if the harassment doesn’t rise to a criminal level, victims are on their own to figure out what to do.

Pew found that 60 percent of those who had been harassed chose to ignore the most recent incident. Of those who responded to the harassment, 47 percent confronted the attacker online, 44 percent unfriended or blocked that person, 22 percent reported the person to the website or online service they were using, and 18 percent discussed the incident online to draw support for themselves. Smaller percentages chose to change their usernames, delete profiles or withdraw from an online forum.

Only 5 percent reported the online harassment to police.

None of that makes the negativity disappear, but people seem to be finding ways to cope.

“No matter which route people took, they were really likely to say that it was effective,” said Maeve Duggan, author of the Pew report.

O’Reilly takes screen shots to document a threatening tweet, but then blocks those who harass her and moves on with her otherwise fulfilling digital life.

“We have to learn to be more respectful,” O’Reilly said. “We also have to learn to know when to just shut it down.”