NATO headquarters started Tuesday, Nov 26, a large-scale cyber defense exercise based largely in Estonia, with participants scattered across 32 other European countries, ERR News reported.

The three-day exercise, codenamed Cyber Coalition 2013, is NATO's largest cyber exercise to date in terms of the number of countries taking part.

Participants include around 400 IT experts, legal specialists and government officials, according to a statement from Estonia's Defense Forces. Over 100 of them are operating from the National Defense College in Tartu and another 300 are based in various staff centers around the continent.

NATO will practice combating simulated cyber attacks against computer networks. Officials will test the experts' response speed, coordination and decision making capabilities.