More than 200 students at the prestigious Hackley Middle School in Tarrytown have been simultaneously infected with a gastro-intestinal virus Wednesday, school officials say.

News 12 Hudson Valley received an anonymous tip about the outbreak of a norovirus at the private institution. Later, the school?s headmaster confirmed the information, saying that about a quarter of the students were sent home or did not attend at all.

School officials say following the outbreak, all common areas on campus, including the cafeteria, have been thoroughly disinfected.

Many parents, however, say they are concerned because they have not been informed about the outbreak of the illness.

According to the Center for Disease Control Web site, a norovirus causes stomach flu-like symptoms, including nausea, vomiting and diarrhea. The virus is highly contagious, but it does not have long-term effects. People infected with the virus usually suffer from symptoms from one to two days.