Deface

[Sarah]

To destroy; to make Null. [Obs.][Profane scoffing] doth . . . deface the reverence of religion.Bacon.For all his power was utterly defaste [defaced]. Spenser.

[Sarah]

To remove a friendship from facebook due to having either accidentily adding him/her as a friend or actually adding them and reconsidering later.

[Sarah]

what a hacker usually does to someone's website

[Vania]

Spoil the surface or appearance of (something), for example by drawing or writing on it.