The report, which Weiss read to The Washington Post, describes how a series of minor glitches with a water pump gradually escalated to the point where the pump motor was being turned on and off frequently. It soon burned out, according to the report.

The report blamed the damage on the actions of somebody using a computer registered to an Internet address in Russia. “It is believed that hackers had acquired unauthorized access to the software company’s database” and used this information to penetrate the control system for the water pump.

Experts cautioned that it is difficult to trace the origin of a cyber-attack, and that false addresses often are used to confuse investigations. Yet they also agreed that the incident was a major new development in cyber-security.

“This is a big deal,” said Weiss. “It was tracked to Russia. It has been in the system for at least two to three months. It has caused damage. We don’t know how many other utilities are currently compromised.”