(CNN) -- Hackers have been busy causing service interruptions, breaching databases, and defacing hundreds of Ukrainian and Russian websites, as the crisis between the two countries plays out in cyberwarfare. The attacks have similarities to the resistance movement that sprung up among German-occupied countries during World War II, which took many forms including sabotage, espionage, armed confrontation and counter-propaganda. In addition to that list, today we can add digital or web-based actions including Distributed Denial of Service (DDoS) attacks, which shut down key websites, the defacement of government websites, and breaching government or key industry networks to access sensitive documents and release them to the world.
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The Ukraine-Russia crisis is playing out in cyberwarfare, says Jeffrey Carr
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Hackers have been causing service interruptions and breaching databases, he says
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Carr says the attacks have similarities to the resistance movement in WWII Europe
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He says the most powerful nations cannot reliably defend their infrastructure from attacks
In 2010, @placeholder published a new military doctrine which acknowledged the "intensification of the role of information warfare" and assigned as a task to "develop forces and resources for information warfare."