In Act 1, Scene 5, the ghost of King Hamlet appears to his son, asking him to avenge his death by the poisoning of his brother. This heinous act of fratricide is, indeed, an act that portrays the corruption of the soul of Claudius. In fact, when the ghost of the king appears to Hamlet, he tells his son that he is doomed to
walk the night.../Till the foul crimes done in my days of nature/Are burnt and purged away (I,v,10-13)
The ghost of King Hamlet entreats his son to "Revenge his foul and most unnatural murder" (I,v,25), describing the effects of the poison that Claudius poured into his ear as causing a white, scaly crust upon his body making him appear leprous. With such a cruelly, abrupt death, King Hamlet is also deprived of the Last Rites of the Church--no communion, no forgiveness of sins, and no anointing. This deprivation of the sacraments of his church is a moral deprivation--a corruption--of his life by Claudius.
Now, King Hamlet, continues, Claudius has wed Hamlet's mother; and begs his son not to let Denmark become "a couch for luxury and damned incest" (I,V,88). To his father's words, Hamlet reacts strongly, referring to his mother as "pernicious woman," while calling Claudius a "smiling damned villain" (I,v,110,111).
This scene ends with Hamlet's saying,
This time is out of joint. O cursed spite/That ever I was born to set it right! (I,v,87-88)
There is a corruption of the natural order of life--"This time is out of joint"--for Hamlet feels that his father should not have so unjustly died. Yet, there is also a hesitancy suggested in his line of cursing that he should have to avenge his father's death, a remark that is in marked contrast to the first reaction of Hamlet to the ghost of his father,
Hast me to know't, that I, with wings as swift/As meditation or the thoughts of love,/May sweep to my revenge. (I,v,29-31)
So, in a sense, there is a corruption of Hamlet's will as he debates with himself in several soliloquies if and when he should avenge his father. And, it is not until the final act, of course, that Hamlet finally does take action.
In Act I scene v, Hamlet hears of his father's Ghost's confession of "foul crimes" and "secrets" of that would "harrow up thy soul" and "freeze thy young blood." Using much biblical imagery and allusion, the Ghost likens his murder to the tale of Original Sin in the Garden of Eden (man's first corruption): he was alone, sleeping in the garden when a serpent put poison in his ear.
The Ghost tells of being confined to Purgatory, a place between heaven and hell where one is punished for sins, but he likens it more to hell: "sulphurous and melting flames," "fast in fires," "burnt and purged," and "uneffectual fire."
When speaking of his late wife and brother, he mentions "serpent stung," "damned incest," "incestuous adulterate beast," "traitorous," and "prey on garbage." They are the two-headed devil-serpent in the garden. He wants his son to seek revenge of his brother but not his wife, "leave her to heaven."
The Ghost says that when his brother snuck up behind him to poison him in the ear he became "lazar-like":
And a most instant tetter bark'd about, / Most lazar-like, with vile and loathsome crust, / All my smooth body.
Upon receiving the poison, King Hamlet breaks out into a scaly rash all over his body, like Lazarus. (Lazarus, as you know, was a leper from the Bible.) There's no greater poster-child for decay than a leper.