New York Police Commissioner Raymond Kelly says international hackers try at least 70,000 times a day to gain unauthorized entry into the computer system of the largest U.S. police force.

But he said Wednesday all the attempts have failed because of a strong protection system that prevents security breaches.

Kelly says the NYPD has documented computers in China, the Netherlands and other countries that illegally scan NYPD computers, looking to hack into the system.

He described the computer threats in a speech to the Council on Foreign Relations.

Kelly says terrorism has remained a threat facing New York City in the years after the Sept. 11, 2001, attacks. The NYPD continues to step up surveillance efforts and expand its international reach.