Hypercorrection is an ungrammatical and misguided attempt at proper grammar. This generally occurs when the speaker attempts to signify a certain learned sophistication or knowledge without possessing any thereof.
One example of hypercorrection occurs in the common confusion between objective and subjective pronouns. Take for example the sentence, "Whom shall I say is calling?" The objective pronoun, whom, serves as the subject of the verb only to elicit sniggers from those who hear the lapse in grammar.