JERUSALEM (JTA) — The Israel Defense Forces has revoked exemptions to some 4,000 men who claimed they were yeshiva students.

The men were found to be living a secular lifestyle or were not studying 45 hours per week at a yeshiva as required, Ynet reported, citing a senior official in the IDF’s Manpower Directorate.

Some of the men have received their reissued military orders, others have begun their service, Ynet reported. Others have appealed the decision and provided proof that they do, indeed, study in a yeshiva.

The IDF has used private investigators to uncover the draft dodgers, and have also discovered Facebook pages which give the young men away with photos showing the men engaging in activities on Shabbat or hanging out with women, which haredi Orthodox men are not permitted to do.

“We give the time to study to whoever needs it. We’ve discovered a lot are registered to a yeshiva, but don’t actually attend. We’ve always enforced—what’s new today is the use of social media in ultra-Orthodox society. We can easily reach them on Facebook and can do a lot of detective work using a smart phone,” the unnamed official told Ynet.