Summary:
Google is collecting evidence indicating that at least around 3% of modern cups are silently corrupting data in ways that users don't notice.
A pathological cpu core is described that performs AES in some way such that it can reliably decrypt its own encrypted documents, but no other discovered cores can do so.
The failures are called "corrupt execution errors" and the invisibly failing cores "mercurial" . Blamed on problems of miniaturization. Chip manufacturers have not spoken yet. Google is finding more problems as they improve their software for detecting them.