Estonia says the country's websites have been under heavy attack for the past three weeks, blaming Russia for playing a part in the cyber warfare.
Many of the attacks have come from Russia and are being hosted by Russian state computer servers, Tallinn says. Moscow denies any involvement.
Estonia says the attacks began after it moved a Soviet war memorial in Tallinn. The move was condemned by the Kremlin.
A Nato spokesman said the organisation was giving Estonia technical help.
"In the 21st century it's not just about tanks and artillery," Nato spokesman James Appathurai told BBC News
"We have sent one of our experts at the request of the Estonian authorities to help them in their defence."