Israeli officials have detected a severe cyberattack that targeted the electric grid earlier this week, Energy Minister Yuval Steinitz said Tuesday. The attack, which has not been blamed for any power outages, occurred Monday and was among the most serious cyberattacks the country has ever reported.

“The virus was already identified, and the right software was already prepared to neutralize it,” Steinitz told 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.”

Parts of the computer system were shut down for two days, the agency later added, though officials have not commented publicly on possible suspects or motive. The attack coincided with a period of cold temperatures, which already created an extra strain on the grid. Israeli officials have previously speculated that Iranian-backed hackers may have been responsible for prior, unrelated attacks.

Israel is widely believed to have partnered with the U.S. to launch the Stuxnet virus in 2010. That attack, aimed at Iranian nuclear centrifuges, is one of the only cyber incidents known to have caused physical damage.

This announcement comes one month after a Ukrainian power plant, part of the country's civilian infrastructure, was knocked offline by hackers, causing an hourslong blackout. That event remains under investigation, though a group of Russian government-sponsored hackers has been named as the primary suspect.