Updated This story was updated with a statement from CA on 2 January
The dodgy update is DAT 5417 released at 02:22 ET (07:22 GMT) on December 31. A fix was released some nine hours later.
Faulty anti-virus signature updates are not uncommon across the industry. The timing of the glitch on New Year's Eve was unfortunate nonetheless the time taken for CA to pull the dodgy update and issue a replacement might be criticised as slow.
Users hit by the slip-up have posted their gripes and compared experiences in various online blogs and forums (example here).