Words

1. disgruntled - angry or dissatisfied
     Judges receive letters from disgruntled members of the public.
     A disgruntled individual sabotages the network by intentionally writing bad code.

2. sabotage - deliberately destroy, damage, or obstruct (something), especially for political or military advantage
      Railway tracks in Rajastan were sabotaged by gujjars union.


3. malicious - intended to do harm
     He was found guilty of malicious damage

4. inadvertent -  not resulting from or achieved through deliberate planning.

"an inadvertent administrative error occurred that resulted in an overpayment"

synonyms:

unintentional, unintended, accidental, unpremeditated, unplanned, unmeant, innocent, uncalculated, unconscious, unthinking, unwitting, involuntary;

5. vigilant - keeping careful watch for possible danger or difficulties.

1. 
   

   "the burglar was spotted by vigilant neighbours"

   
   

   synonyms:

   watchful, on the lookout, observant, sharp-eyed, keen-eyed, gimlet-eyed, eagle-eyed, hawk-eyed, with eyes like a hawk, with one's eyes open, keeping one's eyes peeled/skinned, attentive, paying attention, alert, on the alert, on one's toes, on the qui vive; More