Two months after much of Estonia's online infrastructure was targeted by an online attack, the U.S government is sending cyberinvestigators to help the Baltic state better understand what happened.

A representative from the U.S. Department of Homeland Security's US-CERT (U.S. Computer Emergency Response Team) division is heading to Estonia this week to help analyze the large volume of data that was generated by the attacks, said Gregory Garcia, assistant secretary for cyber security and telecommunications with the DHS. "We are sending someone from our organization ... to help them with forensic analysis and to do some additional training on how to secure their infrastructure," he said.

Additionally, a member of the U.S. Secret Service will be there to help with training on incident response and computer crime investigations, according to a DHS spokesman.

In April, a widespread DDOS (distributed denial of service) attack struck Estonia and affected government and banking Web sites. Early press reports linked the attacks to Russia, exacerbating tensions between the two countries, but investigators now say that it is unclear who exactly was behind the incident.

"The data that we have does not speak to who's behind it. There's no smoking gun," said Jose Nazario, senior security engineer with Arbor Networks Inc., who has studied the attacks.

Unlike other Internet conflicts, the Estonian attacks do not seem to have been backed by a particular hacking group, said Gadi Evron, a security evangelist with Beyond Security. "They were of immense variety [and came] from the population of the Russian-speaking blogosphere," he said via instant message.

Some attackers ran simple scripts on their PCs, while others trained sophisticated groups of botnet computers at the Estonian systems, Evron said. "Many of the attacks were from fake sources and compromised computers around the world," he added.

During the incident, several international organizations helped the tiny country repel the online attacks, Garcia said.

"This was -- at least in the aftermath -- a good news story in the sense that Estonia looked to NATO for assistance and together the NATO countries came to the aid of Estonia," Garcia said. "It showed that the relationships we have internationally and across the federal government are paying off so we can respond in real time to attacks that are happening."

Garcia said that members of US-CERT could learn how the U.S. should respond if faced with a similar attack. "It's a little bit more complicated than conventional warfare," he said. "It's a little difficult to trace back where a particular attack is coming from, which makes it more difficult to respond."

Arbor Networks' Nazario agreed that investigators will get a much clearer picture of how the attacks evolved over time. "They can basically learn what ... technologies and what techniques worked under those attacks," he said.