By Pat Loeb

PHILADELPHIA (CBS) — Cyber attacks are potentially the biggest risk to security the country faces, according to Homeland Security secretary Janet Napolitano.  That’s what she told a conference of security professionals this afternoon at the Pennsylvania Convention Center.

Napolitano says she has made cyber security a focus of her department.

“The threats are real and they are ever-evolving,” she told the American Society for Industrial Security at its convention today in center city Philadelphia.  “They are serious, and they go to the heart of the success and safety of our communities and our economies.”

Napolitano says federal computer systems receive thousands of threats every year and hackers are targeting water companies, natural gas pipelines, and the nuclear and chemical industries.

She told the group that one challenge she faces is that most computer networks are private, and she asked for cooperation to make them secure.

“My friends, we are all in this together.  We all need a safe and secure cyberspace.  We have to work together to get to where we need to be, in as quick a time as possible,” she said.