FBI director Robert Mueller warned a gathering of Internet security specialists on Thursday that the threat of cyber-attacks rivals terrorism as a national security concern.

The only way to combat cyber assaults is for police, intelligence agencies and private companies to join forces, Mueller said during a presentation at an annual RSA Conference in San Francisco.

"Technology is moving so rapidly that, from a security perspective, it is difficult to keep up," Mueller said. "In the future, we anticipate that the cyber threat will pose the number one threat to our country."

It's essential that private corporations and government agencies across the globe coordinate on cyber-crime, Mueller said, in part because nefarious hackers are already forming alliances.

"We must work together to safeguard our property, to safeguard our ideas and safeguard our innovation," Mueller said. "We must use our connectivity to stop those who seek to do us harm."

Gone are the "good old days" of teenage boys hacking into websites for fun, Muller said. Today's hackers are savvy and often work in groups, like traditional crime families.

Private sector computer security researchers have attributed waves of cyber assaults to nations out to steal government or business secrets.

"Once isolated hackers have joined forces to form criminal syndicates," Mueller said.

Those "syndicates" often operate across borders, posing a particular problem for government agencies that are constrained by conflicting justice systems and a lack of coordination with foreign agencies, he said.

"Borders and boundaries pose no obstacles to hackers, but they continue to pose obstacles for global law enforcement," he said.

In a presentation that a subsequent speaker said "really scared the bejeezus out of us," Mueller emphasized an overlap between the violent terrorism the FBI has focused on since September 11 and today's world of cyber-crime.

Terrorist organizations like al-Qaida and al-Shabaab in Somalia are "increasingly cyber savvy," he said.

Mueller referenced al-Qaida's English-language online magazine and al-Shabaab's Twitter account, which he says the group uses to recruit and encourage terrorism.

"They are using the Internet to grow their business and to connect with like-minded individuals," he said.

Mueller warned that no company is immune from cyber-attack.

He argued that it's in the best interest of private companies to share information about online assaults with government agencies fighting the hackers.

The nation's top cop promised that the FBI would "minimize disruption" and protect the privacy of corporations as it investigated cyber threats.

Companies are often reluctant to report network security breaches out of fear that the publicity could tarnish images in the eyes of customers or erode shareholder confidence.

"Maintaining a code of silence will not serve us in the long run," Mueller said. "For it is no longer a question of 'if' but when and how often."

"We are losing money, we are losing data, we are losing ideas," he added. "Together we must find a way to stop the bleeding."