PITTSBURGH (AP) A 20-year-old off-campus student has been jailed on charges that he posted a social media threat to shoot people at a popular gathering area on Penn State's main campus.

Jong Seong Shim, of Tinton Falls, New Jersey, told police on the campus about 140 miles east of Pittsburgh that his post on the social media site Yik Yak was a "prank," according to a criminal complaint filed Monday by campus police.But Police Chief Tyrone Parham said in a statement that, "Alarming an entire community is not considered a joke."The sophomore engineering student was jailed after he was unable to immediately post $100,000 bond following his arraignment on two counts of making terroristic threats and one count of disorderly conduct. The message was posted about 10:30 p.m. Saturday threatening to shoot people at the HUB, a center of campus social life that includes various eateries and other places students meet to socialize. Several students alerted campus police when they saw the post.Yik Yak is a social media service that enables users to post anonymous comments that are deleted a short time later, and visible only to those within 1.5 miles of the poster, university police said.Police took the threat seriously since it targeted the HUB, where there likely would be large numbers of people. Police had planned to have additional officers on patrol before they were able to trace the post to a mobile device used by Shim."I am going to kill everyone in penn state main on Monday. I got 5 bet mags of ar 15 and shoot everyone in the hub at 12:00," the post said, referring to ammunition and a type of rifle known as an AR-15. "This is a warning."Police said they worked with Yik Yak officials to identify the mobile device used to post the message as well as Shim's location when that occurred.There were no weapons, or any other indication that Shim planned to carry out the threat, in his off-campus apartment, police said."We are grateful to our very alert and diligent students who first discovered this threat and raised their concerns with police," Steve Shelow, Penn State's assistant vice president for Police and Public Safety said in a statement.Students remain concerned. "There have been numerous campus threats all over the country made via YikYak," said Jillian Murray, a junior from Brodheadsville."Apps like this, although fun at times, shouldn't be allowed on college campuses if they're going to interfere with the learning environment of college communities. With that being said, Penn State police did a superb job keeping its students informed and resolving the situation quickly."Kasey Feather from Clarks Summit said, "I've heard people talking about the Yik Yak post as an empty threat and I think it's scary to think that posts like these are made and students aren't worried about taking any extra precaution."Feather added, "With all that's happened in the past regarding threats like these, you'd think people would be more careful, regardless if the man is in custody or not."Jordan Reabold contributed to this report.