Chinese and Russian hackers are attempting to seed viruses in the US power grid that could one day plunge major cities into chaos, a report warned Wednesday.

The report in the Wall Street Journal quotes intelligence officials saying that cyber-spies last year repeatedly gained access to the system powering everything from financial institutions to sewage systems.

Barack Obama, the most Internet-savvy president in US history, has pledged to expand the use of the Internet across the country. Among the projects is a major overhaul, with increasing reliance on computer networks, of the electric grid.

That adds to pressure to defend against the growing army of cyber assailants.