Israel experienced a serious hack attack on its electrical grid that officials are still working to repel, the head of the country’s energy minister said Tuesday.

“The virus was already identified and the right software was already prepared to neutralize it,” Israeli Energy Minister Yuval Steinitz told attendees of a computer security conference in Tel Aviv, according to this article published Tuesday by The Times of Israel. “We had to paralyze many of the computers of the Israeli Electricity Authority. We are handling the situation and I hope that soon, this very serious event will be over … but as of now, computer systems are still not working as they should.”

The “severe” attack was detected on Monday as temperatures in Jerusalem dipped to below freezing, creating two days of record-breaking electricity consumption, according to The Jerusalem Post. Steinitz said it was one of the biggest computer-based attacks Israel’s power infrastructure has experienced, and that it was responded to by members of his ministry and the country’s National Cyber Bureau. The energy minister didn’t identify any suspects behind the attack or provide details about how it was carried out.