An account circulates that the leap second inserted on 30 June 2012 caused simultaneous failures across unrelated operators, through a kernel path that spun when the clock stepped. No claim is made here about which operators were affected, which kernel versions carried the defect, or whether the failures shared one cause.
Editorial judgements on a 0 to 10 scale, argued in the notes below and nowhere else. They order a list. They are not evidence and they never appear in a claim.
Treat a clock that can step, repeat or stall as a hostile input, and never let a wait be bounded by a wall clock you do not control.
Triage questions. This one is unusual for the inbox because primary evidence probably exists: operator post-mortems published at the time, and the kernel commit that fixed it. Find the commit and read what it says the defect was, rather than accepting the summary that circulates. Establish which reported outages actually shared that cause and which were merely contemporaneous, because simultaneity is the thing a good story will quietly convert into causation. Worth promoting early: it is the inbox's best chance at a record whose explanation is supported rather than hypothetical.