RALEIGH Two reports this week of possible men with concealed guns on the campus of N.C. State University stemmed from students playing a game called Humans vs. Zombies that has become a phenomenon on U.S. college campuses in recent years, university police said Friday.

"NC State police have determined that both reports of individuals on campus who might be carrying handguns were related to the Humans vs. Zombies game, and that there was no threat to campus. Both incidents were related to the same individual, who contacted police after hearing the descriptions and locations," police said in a statement.

They did not identify the student.

Though it was a game, police said they "thank those individuals who witnessed suspicious behavior and contacted authorities."

The game is now so popular that it has a website: humansvszombies.org .

As it describes the game, "Humans vs. Zombies (HvZ) is a game of moderated tag played at schools, camps, neighborhoods, military bases, and conventions across the world. Human players must remain vigilant and defend themselves with socks and dart blasters to avoid being tagged by a growing zombie horde."

Students at Goucher College in Baltimore are widely credited with having invented the game in 2005.

The N.C. State incidents Wednesday caused police to issue a security alert, even though they suspected it might be game players.

A day earlier, Wake Technical Community College had a lockdown after police had a credible threat that someone with a gun was driving to the school's main campus to hurt someone.

They made an arrest in that case.

Guns on college campuses have become a threat that all police take seriously since a gunman killed 32 people and wounded 25 at Virginia Tech in 2007.