And as Reuters describes in fascinating detail, the 31-year-old information security researcher and post-doctoral fellow at Austria's Graz Technical University had just breached the inner sanctum of his computer's CPU and stolen secrets from it.
Until that moment, Gruss and colleagues Moritz Lipp and Michael Schwarz had thought such an attack on the processor's 'kernel' memory, which is meant to be inaccessible to users, was only theoretically possible.
"When I saw my private website addresses from Firefox being dumped by the tool I wrote, I was really shocked," Gruss told Reuters in an email interview, describing how he had unlocked personal data that should be secured.
Gruss, Lipp and Schwarz, working from their homes on a weekend in early December, messaged each other furiously to verify the result.
"We sat for hours in disbelief until we eliminated any possibility that this result was wrong," said Gruss, whose mind kept racing even after powering down his computer, so he barely caught a wink of sleep.