Israel's National Cyber Directorate on Tuesday night warned that many Israeli WhatsApp accounts have been hacked.

"We have received several reports of private accounts being hacked," the Prime Minister's Office said in a statement.

The security breach was first recognized by Israeli security expert Ran Bar-Zik.

It occurs via the cellular phone's voicemail, affecting customers who did not change the voicemail password from the default.

It is not clear if the hackers used the voicemail's security breach while hacking Israeli accounts on Tuesday. However, the Directorate suggests changing the voicemail password and enabling WhatsApp's two-step verification.