I don't think this needs to be covert anyway. Think of the damage full doxxing could do to Russian government officials, releasing bank accounts, passwords, Russian equivalent of Social Security Numbers, etc. They need to up this and go further down the chain and target governors and mayors, etc. too.
That would be a clear act of war which, given what we know about Putin's personality, will lead to an escalation. Such tactics are the best way to unite the entire Russian people around their government. Imagine "independent" Russian hackers paralyzing Wall Street banks even for a few hours - the consequences will be global.
No, the response should be firm but still low enough that Putin won't be able to escalate it. Maybe another story about Putin secretly owning mansions in London and bank accounts in Geneva. Lots of Russian oligarchs own condos in Miami and Fort Lauderdale - maybe a few tax inspections are in order...