The Lithuanian, Latvian and Estonian power grids have all been targeted by Russia undergoing a series of limited Distributed Denial of Service (DDoS) over the last few years that may be probing for weaknesses.

A Reuters story said law and utility officials from the three NATO members said DDoS attacks have been launched by Russia against different internet gateways that are used to control the power grid for the Baltic area. The unnamed sources also reported attacks against network communications devices that link power sub-stations to central control and a separate attack targeting a petrol-distribution system.

In no case was power disrupted or any damage done.

"On a daily basis there are DDoS attacks designed to probe network architecture, so it could well be possible that something (serious) could take place later on," a Brussels-based NATO official told Reuters, requesting anonymity because he was not authorized to speak publicly on the matter.

The news agency quoted a Russian spokesman who called the allegations slanderous.