Department of Homeland Security’s Industrial Control Systems Cyber Emergency Response Team, or ICS-CERT said he systems are vulnerable because they are exposed to the Internet.
ICS-CERT spokesman Marty Edwards said that more hackers were gaining access to that control system layer.
ICS-CERT helps US firms investigate suspected cyber attacks on industrial control systems as well as corporate networks.
The issue has gained attention after Ukraine authorities blamed a power outage on a cyber attack from Russia, which would make it the first known power outage caused by a cyber attack.
Experts attending the S4 conference of some 300 critical infrastructure security specialists in Miami said the incident has caused U.S. firms to ask whether their systems are vulnerable to similar incidents.
Edwards said he believed the increase in attacks was mainly because more control systems are directly connected to the Internet.
“I am very dismayed at the accessibility of some of these networks… they are just hanging right off the tubes,” he said in an on-stage interview with conference organizer Dale Peterson.
Edwards did not say whether those attacks had caused any service disruptions or threatened public safety.