MOSCOW—The sanctions imposed by Washington on Moscow’s top intelligence services has sharpened the focus on the links between Russia’s security services and the world of black-hat hacking.

The Kremlin, which has consistently denied any government involvement in the cyberattacks, promised a retaliation. Though it isn’t clear whether the Russians will respond with tit-for-tat diplomatic expulsions, Russian officials have repeatedly said they would have no other response to such measures by the U.S.

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