NATICK (CBS) – The Natick superintendent of schools is warning parents to monitor their children’s social media activity for a new game that challenges participants to harm themselves.

Superintendent Peter Sanchioni sent parents a letter on Thursday about the “Blue Whale Challenge,” which he called “very concerning” for targeting a “very vulnerable population.”

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“The Blue Whale Challenge is an app that instructs its participants (many preteens) to carry out increasingly dangerous tasks and self-harm over 50 days,” Sanchioni wrote. “Users are encouraged to tag friends on social media and ‘challenge’ them to participate in the game.”

According to a USA Today article from earlier this year, challenges start with something as simple as watching a scary movie.

But the tasks escalate to things like cutting, and by the 50th day participants are supposed to commit suicide.

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Social media platforms like Instagram, Snapchat and YouTube can be used for the game.

Parents are asked to talk to their children about any new games or challenges their friends may be playing.

Sanchioni also encouraged parents to search their children’s social media accounts for use of the #BlueWhaleChallenge hashtag or photos of a blue whale.

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“This post is not meant to alarm anyone, but rather to encourage parents to be proactive in protecting their children from potential negative influences on the internet,” Sanchioni wrote.