The attacks were launched last year after Estonian officials removed a bronze statue memorialising Soviet soldiers. The act prompted backlash among the country's ethnic Russian population and lead to a series of protests in which one person was killed.
The move also prompted an unprecedented effort in cyberspace. Russian hackers mobilised in late May to cripple Estonian government websites.
The attacks were initially blamed on the Russian government, which was alleged to have emplyed the use of botnets to conduct the assult.
However, Moscow was cleared after the attack was found to be the work of a flash mob organised online and armed with special tools designed to take down the government sites.