TARTU, Estonia (AP) — Thirty-three countries are attending NATO's largest ever cyberdrill in Estonia, focusing on malware in tablets and how infected devices may compromise data privacy for staff of the world's biggest military alliance.

U.S. Navy Cmdr. Robert Hoar, who heads the drill, on Thursday said scenarios do not include "attacking or defending;" participants have instead been provided realistic "storylines" that must be solved.

The five-day Cyber Coalition 2015 exercise, held at the alliance's cyber exercise range in Estonia's second city, Tartu, mainly aims at enhancing NATO nations' ability to work together in a crisis situation.

NATO Cooperative Cyber Defence Centre of Excellence — a think-thank and training facility — is based in Tallinn, the Estonian capital. It is the third time that the small Baltic nation is hosting such an event.