Harassment. Physical threats. Bigotry. Hate has become an almost unavoidable fact of life on the internet.

More than half of Americans – 53 percent – say they were subjected to hateful speech and harassment in 2018. And 37 percent reported severe attacks, including sexual harassment and stalking, according to a survey released Wednesday by the Anti-Defamation League, a nonprofit which tracks and fights anti-Semitism. For a third of Americans, online abuse was in response to their sexual orientation, religion, race, ethnicity, gender identity or disability, the survey found.

"This is an epidemic and it has been far too silent," said Adam Neufeld, ADL's vice president of innovation and strategy. "We wanted to understand the extent of it and the impact of it."

The results seem to show a sharp increase from the 18 percent of Americans who reported online harassment in a 2017 survey by the Pew Research Center, and that startled Neufeld.

"This was significantly worse than we expected," he said.

The ADL survey is the most recent to capture a growing wave of toxic rage that's traumatizing internet users and normalizing deeply offensive points of view that would otherwise be relegated to the darkest corners of the internet. Swarms of attacks, often anonymous, feed off a tense and polarized political climate in which inflammatory social media posts can draw attention and spread quickly.

Threats online can spill over into real-world violence and turn deadly. Robert Bowers, who allegedly killed 11 people at a Pittsburgh synagogue in 2018, regularly posted anti-Semitic and neo-Nazi propaganda on Gab, a social network frequented by right-wing extremists. Cesar Sayoc, who's accused of mailing homemade explosive devices last year to critics of President Donald Trump, made repeated threats against public figures on Twitter.

More than one in five respondents in the ADL survey reported being subjected to physical threats online and nearly one in five experienced sexual harassment (18 percent), stalking (18 percent) or sustained harassment (17 percent).

Some of those surveyed said they were targeted because of their identity. Of those who experienced online harassment, 20 percent said it was the result of their gender identity, 15 percent the result of their race or ethnicity, 11 percent their sexual orientation, 11 percent religion, 9 percent occupation and 8 percent disability.

The reverberations can linger long after online attacks. Thirty-eight percent of the individuals surveyed who experienced online hate or harassment said they curtailed or changed their online habits while 18 percent tried to contact the social media platform, 15 percent took steps to protect themselves and 6 percent contacted the police to ask for help or report the harassment.

The millions of hateful posts and videos polluting their platforms represent one of the most pressing challenges for Facebook, Twitter, Google's YouTube and other technology companies. Measures such as hiring thousands of moderators and training artificial intelligence software to root out online hate and abuse have not yet solved the problem. Algorithms still struggle to accurately interpret the meaning and intent of social media posts while moderators, when reviewing posts, frequently stumble, too, missing important cultural cues and context.

The overwhelming majority of respondents to the ADL survey, regardless of political affiliation and whether they have personally been harassed, said they want lawmakers and technology companies to take more aggressive steps to counter online hate and harassment and keep users safe.

Some 80 percent of those surveyed believe government should strengthen laws against online hate and harassment and improve training and resources for law enforcement. Three-quarters of them want tech companies to make it easier to report hateful content and behavior and 81 percent want companies to provide more ways to filter out the content. Most Americans say tech companies should label comments and posts that appear to come from automated accounts or "bots."

"What gives the ADL hope is that there is a wide cross section of Americans who want to deal with this problem and want real action from government and from tech companies," Neufeld said.

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The ADL survey of 1,134 Americans was conducted in December by YouGov, a public opinion and data analytics firm. It found: