The way witches deal with evil is not to destroy, but to transform it.  Negative energy is transformed to positive energy.  This is how exorcisms are performed, the way healings are performed and the way psychic attacks are repelled.

Psychic attack comes through the invisible.  This can be from invisible beings or sent from incarnate beings, from ordinary people thinking negative thoughts,or it may be sent by practitioners of any number of negative traditions.  Also one might consider that of the Threefold Law, whereby negative work directed at another person might be the reason for having triggered a psychic attack.  Whether they are sent on purpose or accidently they are all a product of negative energy.

Psychic attack takes all forms:  Some manifest as illness, depression, an accident, fire or flood of mysterious causes,  unwanted vermin or bugs, unpleasant smells or sounds and even negative hauntings.  Feeding on feelings of vulnerability and fear, there is always a mood of strangeness that goes with it.

Words of Power are the cure.
Goddess and God Alignments the antidote.
Rest and special consideration for yourself is the aftercare, along with wearing the Craft jewelry, carrying crystals, visualisation of your protective shield, consulting the oracles regularly, Words of Power and frequently repeating Alignments are good to aid the prevention of a further attack.
Words of Power bounce the psychic attack back to sender transforming negative energies to positive.  Since the energies of the Universe may be seen as "Neutral", the sender of the attack worked to change the neutral energy to negative.  When dealing with this energy at its basic level, the witch transforms all the energy to positive and any energy that still insists on remaining negative will be returned to sender.
This explanation comes from Marion Weinstein in her book "Earth Magic".  The following Words of Power for Repelling a Psychic Attack are as follows:

By the One Power
Working for me and through me,
I am divinely protected and perfectly safe;
My loved ones are all divinely protected and perfectly safe,
According to Free Will and for the Good of All
In all time and all space,
I hereby release
All cause, all manifestation, all form and all essence
Of everything and anything negative --
Specifically having to do with psychic attack,
I specifically release all cause, effect, manifestation, form or essence of anything having to do with ( name symptoms or problems of psychic attack).

All of this and anything else negative, named or un-named,
Is dissolved and released and turned to good, in my life and the lives of my loved ones.
In the names of my Deities.
In the name of you, Diana, Selene, Hecate, Kernunnos and Pan,
All psychic attack is gone, And I am free;
And so mote it be.

Note, you can name Deities of your own choice.

Remember - human perception may have decreed that there is good versus evil, but this is perception only.
By readjusting our perception - there is no evil power to combat.  It is simply Neutral Energy once coloured Negative, now to be RE-DEFINED.
As Marion Weinstein puts it, the Positive power the witch uses to do this is no less powerful than the negative power  the Perpetrator drew upon.  In fact, the use of the positive power is stronger, because it is not burdened with the trappings of the negative, which is ultimately SELF-DESTRUCTIVE.

As the I Ching explains:
               The dark power ...in the end...perishes of its own darkness, for evil must itself fall at the very moment when it has wholly overcome the good, and thus consumed the energy to which it owed its duration...