The Jargon File (version 4.4.7, 29 Dec 2003):

hacked off
 adj.

    [analogous to ?pissed off?] Said of system administrators who have become
    annoyed, upset, or touchy owing to suspicions that their sites have been or
    are going to be victimized by crackers, or used for inappropriate,
    technically illegal, or even overtly criminal activities. For example,
    having unreadable files in your home directory called ?worm?, ?lockpick?,
    or ?goroot? would probably be an effective (as well as impressively obvious
    and stupid) way to get your sysadmin hacked off at you.

    It has been pointed out that there is precedent for this usage in U.S. Navy
    slang, in which officers under discipline are sometimes said to be ?in hack
    ? and one may speak of ?hacking off the C.O.?.


The Free On-line Dictionary of Computing (30 December 2018):

hacked off

    (Analogous to "pissed off") Said of system
   administrators who have become annoyed, upset, or touchy
   owing to suspicions that their sites have been or are going to
   be victimised by crackers, or used for inappropriate,
   technically illegal, or even overtly criminal activities.  For
   example, having unreadable files in your home directory called
   "worm", "lockpick", or "goroot" would probably be an effective
   (as well as impressively obvious and stupid) way to get your
   sysadmin hacked off at you.

   [Jargon File]

   (1996-08-26)