Top U.S. government officials have been targeted by hackers through Facebook’s WhatsApp messaging application.

An internal investigation by WhatsApp found numerous U.S. officials in at least 20 countries have become victims of data breaches through hacking software through the app. The hackers allegedly took control of users’ smartphones in order to access data.

The investigation comes as WhatsApp recently filed a lawsuit against Israeli developer NSO Group claiming the group created and sold a hacking platform that exposed a WhatsApp server flaw. WhatsApp officials said those who purchased the platform gained access to about 1,400 user smartphones starting in April.

In response to the lawsuit, NSO said it sells it spyware solely to government buyers.

WhatsApp officials said those affected in the hack have been notified. Along with U.S. officials, victims of the data breach possibly include journalists, activists, and academics from U.S.-allied countries.