The activist, Konstantin Golo-sko-kov, told The Moscow Times that he led a group of several dozen "IT specialists" in attacking the web sites in late April 2007.
"This was an answer to the policy of soft apartheid that the Estonian government has conducted for years," Goloskokov said, referring to claims that Estonia discriminates against its Russian-speaking population.
Goloskokov said his group had acted on its own, not with Nashi. He also said the attack was not illegal because it did not involve hacking.
Several government web sites went down for hours as a result of so-called DDoS attacks -- multiple requests from thousands of computers across the globe triggered by a computer virus, Estonian authorities have said.
Goloskokov said he used "a -special program," not a computer virus.
Estonia has accused the Russian government of being behind the cyberattacks, a charge it has denied. The attacks followed riots by Russian speakers in Tallinn as authorities relocated the World War II monument from a central square.
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