WASHINGTON - President Obama issued an executive order Wednesday allowing the Treasury Department to impose financial sanctions on Internet attackers who pose a threat to U.S. national security.

Saying that online and computerized threats "pose one of the most serious economic and national security challenges to the United States," the president announced sanctions such as freezing attackers' financial assets.

"We're giving notice to those who pose significant threats to our security or economy by damaging our critical infrastructure, disrupting or hijacking our computer networks, or stealing the trade secrets of American companies or the personal information of American citizens for profit," Obama said in a written statement.

The new order declared a national emergency on online threats. It authorized the treasury secretary, working with the attorney general and the secretary of state, to penalize individuals or entities that "engage in significant malicious cyberenabled activities" that threaten the nation's security or economy.

In a separate statement, Treasury Secretary Jack Lew said the order would allow the United States to "expose and financially isolate those who hide in the shadows of the Internet to conduct malicious cyber activities." The primary focus of the order is threats from overseas.

The administration could freeze assets of attackers, block their property in the U.S., or stop them from transferring funds.

In addition, people who use or receive information stolen through online attacks - or those who assist such attackers - could receive sanctions.

The announcement came after the massive attack on Sony Pictures last November, during which attackers leaked internal documents such as employee payrolls, unreleased films, and confidential correspondence.

In an official statement, the FBI said the North Korean government was responsible for the attack.