HADERA, Israel — When Israel’s military chief delivered a high-profile speech this month outlining the greatest threats his country might face in the future, he listed computer sabotage as a top concern, warning a sophisticated cyberattack could one day bring the nation to a standstill.

Lt. Gen. Benny Gantz was not speaking empty words. Exactly one month before his address, a major artery in Israel’s national road network in the northern city of Haifa was shut down because of a cyberattack, cybersecurity experts tell The Associated Press, knocking key operations out of commission two days in a row and causing hundreds of thousands of dollars in damage.

One expert, speaking on condition of anonymity because the breach of security was a classified matter, said a Trojan horse attack targeted the security camera system in the Carmel Tunnels toll road on Sept. 8. A Trojan horse is a malicious computer program that users unknowingly install that can give hackers complete control over their systems.

The attack caused an immediate 20-minute lockdown of the roadway. The next day, the expert said, it shut down the roadway again during morning rush hour. It remained shut for eight hours, causing massive congestion.

The expert said investigators believe the attack was the work of unknown, sophisticated hackers, similar to the Anonymous hacking group that led attacks on Israeli websites in April.