The campaign, which has forced many websites to shut down and inflicted losses on the nation's economy, is being described as the first "war in cyberspace."
The virtual attacks occurred in parallel with unrest in the physical world. They began within hours of the relocation of a Soviet-era war memorial out of the center of Tallinn on April 29, an event which touched off protests in Moscow and by Estonia's Russian community.
The cyberattacks then reached a peak on May 9 -- Victory Day in Russia. The last major wave came on May 18.
"You couldn't get information; you couldn't do your job. You couldn't reach the bank; you couldn't check the bus schedule."
The hackers have been using a simple tactic: sending huge amounts of information to the targeted websites simultaneously, causing them to overload and freeze in what is known in the industry as "distributed denial-of-service disruptions."
To prevent further attacks, Estonia had to close off parts of its network to computer users outside the country, isolating itself from the rest of the Internet.
Tuuli Aug, an editor of international affairs at the Estonian daily newspaper "Eesti Paevaleht," says that she felt the country was under attack by an invisible enemy.
"It was extremely frightening and uncontrollable because we are used to having Internet all the time and then suddenly it wasn't around anymore," she says. "You couldn't get information; you couldn't do your job. You couldn't reach the bank; you couldn't check the bus schedule anymore. It was just confusing and frightening, but we didn't realize it was a war because nobody had seen anything like that before."
The Cost of Cyberwar
Aug says that although cyberattacks leave no bomb holes in the ground, the economic losses are real. Those losses have yet to be calculated, but there is no doubt they are in the millions of dollars. Just one institution, Estonia's Hansabank, reports that it lost at least $1 million because of the attacks.
Estonian Defense Minister Jaak Aaviksoo said in an interview that the attack could be compared "to when your ports are shut to the sea."
Estonia's Defense Ministry says the attacks originated from Russia, some even from official Russian government and security-service sites.
Russia denies it was involved, and it is difficult to prove the Kremlin's involvement in a murky virtual world where computer users can hide behind fake identities all over the world.
For now, most of the attacks seem to be over. However, Aug says the country still needs time to recover. She also says a feeling of security has been lost.
"Currently there are no attacks, but I am sure that if Estonia does anything that Russia doesn't like, the attacks will continue. Now, they are stopped because the [Estonian] defense got better," she says.
Serious Security Issue
Western experts say Estonia employed the right defenses to stop the hacking campaign.
Peter Kratochvil, who works for the Czech Institute of International Relations, is closely following the Estonia-Russia exchange, and says Estonia has managed to win a propaganda war against Russia. At the same time, he says, the conflict has convinced Western security experts that "cyberwar" needs to be taken seriously as a future threat.
"What is important is that this kind of activity is now seen as a kind of hostile act," Kratochvil says.
Computer security experts from NATO, the European Union, the United States, and Israel have been visiting Tallinn to offer help, as well as to improve their own understanding of "cyberwar."
NATO Secretary-General Jaap de Hoop Scheffer said the attacks were a security issue that concerns NATO, of which Estonia is a member. He also said the issue "will stay on the political agenda in the times to come."
In the United States, the deputy assistant secretary of defense for networks and information integration at the Pentagon, Linton Wells II, told "The New York Times" that what happened in Estonia "may well turn out to be a watershed in terms of widespread awareness of the vulnerability of modern society.”