The prefix 'MAL-' in words like MALFUNCTION and MALADY indicates:

The prefix MAL- means bad, badly, or wrong. A MALFUNCTION is a faulty or bad operation; a MALADY is an illness (a 'bad' condition); MALICE is ill will; MALNUTRITION is poor nourishment. Knowing common prefixes lets you decode unfamiliar words on the test. MAL- consistently signals something bad or defective, so when you see it leading a word you don't know, you can infer a negative meaning. Other useful prefixes include BENE- (good), MIS- (wrong), and DIS- (not/opposite). Recognizing MAL- = bad narrows down the meaning quickly.