WEST ISLIP, N.Y. — A community reeling from the suicide of a popular high school senior turned its sorrow to outrage Friday over a practice known as “trolling,” in which derogatory, hurtful comments are posted online against a person.

In this instance, a tribute site created for Alexis Pilkington, 17, of West Islip High School was the target of insulting messages after her death.

“I think it’s horrible. It’s vicious. It’s cruel. It upsets me as a parent,” Lorraine Kolar said as she left a memorial service Thursday for Pilkington.

Classmates, relatives and friends were incensed over what they called creepy, insensitive messages about Pilkington, many posted anonymously and also appearing on other Internet sites since her death.

“It’s a disgrace,” said Cathi Musemeci, a close friend of the family. “I think it’s horrible. Let the girl die in peace.”

“Trolling is part of the dark side of cyberspace,” said Anne Collier, co-director of the Salt Lake City-based Connectsafely.org, a forum about safety issues on the Internet and social Web sites.

“It’s not necessarily tied to any school activity,” she said. “It’s quite anonymous and random and is usually seen as aggressive, egregious cruelty on the Internet.

“The people who sit behind computers and do this are known as trolls.”