Online gamers are becoming targets of harassment by extremists, according to a study by the Anti-Defamation League.

Eric Donaldson of Hewlett has been an avid online gamer since he was a child, but says friendly competition turned into harassment about eight years ago.

"Every swear word you can imagine," Donaldson says. "Every derogatory term, every racist remark, homophobic remark."

The study found that 65% of online gamers have experienced harassment while playing online games. Those incidents included physical threats, stalking and sustained harassment.

The survey also found that many online gamers were exposed to extremist groups, such as white supremacists and ISIS, looking to normalize hate and recruit new members.

Dr. Nicholas Kardaras, an addiction expert who studied the impact of screen technology on children, says those gamers usually prey on younger people.

"They look for young, isolated, fragile young teens that are looking for meaning and purpose in their lives," Kardaras says. "And so they're the low-lying fruit for a lot of different radical groups.

The study comes while major social media platforms like Facebook and Twitter are dealing with the spread of hate speech and disinformation.

Experts say it's difficult for some children to recognize harassment and indoctrination online. They advise parents to monitor their childrens' online use and to be aware of any changes in behavior.