Not sure on the validity of this claim, but one guy in trade chat was going on yesterday.

Basically said he had been hacked in the past, talked to billing on the phone.
And had them allow his account to be logged in from one of two IP addresses.
But made it impossible to log in, from any other IP.

Not sure if Blizzard has anything like this.
But if they do, that would be the ultimate in security.