The University of Pennsylvania is forming a task force to look into "underground" fraternities and sororities after one such group sent a party invitation to freshmen women that was sexually suggestive.

University officials tell Philly.com (http://bit.ly/2ePgeL2 ) that some students on campus were upset by the invitation and posted copies of it around campus, prompting the school's response.

Underground fraternities and sororities aren't affiliated with the school or its Greek system, though their members are students and the groups are sometimes formed by members of groups that have been banned from campus for violating school or fraternity rules.

School spokesman Stephen McCarthy says the scope and duration of the task force review isn't clear, but the group will include faculty, administrators and students.

The school says the groups engage in "high-risk" behaviors.

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Information from: Philly.com, http://www.philly.com/