The FBI and Department for Homeland Security (DHS) are investigating the incident as details emerge of what could be a separate second attack.
Experts said the news revealed a growing interest in critical infrastructure by cyber criminals.
The comments by the DHS prompted a hacker using the handle "pr0f" to claim he had access to the control systems for a second US water utility.
SOURCE : http://www.bbc.co.uk/news/technology-15817335