Re: Oh yeah
but the insurance company is going to have to prove that in court.
IANAL, however in civil court you don't have to 'prove' something to the same standard as criminal courts - beyond a reasonable doubt. All they would have to show is "on the balance of probabilities" or "more likely than not". So if it is commonly thought by experts that it was likely Russia, then that standard has been met.
Also, again they wouldn't have to prove anything, they'd just need enough to persuade a judge (if bench trial) or jurors (if jury trial). It's not like it's a scientific discovery that requires 5-sigma to be considered proven. Just enough people to believe it.