Synonyms for Malicious (same or very similar meaning)
WordNet sense 1 (marked by deep ill will; deliberately harmful):
poisonous, vicious
WordNet sense 2 (wishing or appearing to wish evil to others; arising from intense ill will or hatred):
malevolent
WordNet sense 3 (showing malicious ill will and a desire to hurt; motivated by spite):
spiteful
From the ODE community, based on WordNet
add/edit