Near-instant account breach

[quasipolymath]

I installed Minion last night, updated a few addons, logged in and out of WoW and went to bed. This morning, my battle.net creds were cleared, all of my toons had been logged into and my account was on temporary ban. Checking last login times indicates that it was less than three hours after I installed and used Minion. I'm livid. I should note that I would be less willing to point fingers if this hadn't happened on a fresh windows install on which I have only installed Symantec Endpoint, Firefox, WoW, Curse Client, and Minion. Everything else was installed over a week ago. Seriously, what the hell is going on here?