The account of administrator User:Robdurbar on English Wikipedia went rogue in the early hours of this morning. Rob had made a friendly goodbye message about six weeks ago and hadn't been active since then.
Between 0957 and 1014 UTC, the account deleted the main page as well as several articles: "History", "Cheese", "Esteban Huertas, "Pita, Guinea", "Balham railway station" and "Mardi Gras Mystery". It also vandalized the main page and blocked several prominent editors including User:Jimbo Wales.
The account was blocked by User:Sarge_Baldy at 1013 UTC, but unblocked itself and blocked the blocker. At 1014 User:Jon_Harald_Søby, apparently having been notified on IRC by User:Peter_Isotalo through #wikimedia-stewards, desysopped the Robdurbar account on English Wikipedia, and the account was finally blocked indefinitely by User:Cryptic. As a formal matter, a checkuser request has been made for the disabled account.
Overall, this incident was handled very promptly and efficiently. Well done and I think a word of appreciation is due to all the volunteers involved.
The worst damage here was the loss of the main page for about fifteen minutes, and the accompanying scrabbling between Robdurbar deleting it and other administrators restoring it.