"Malware" broadly encompasses the various types of malicious software 'in the wild', such as:

• Virii, Worms and Trojans
• Spyware (marketing companies trying to keep track of your habits)
• Redirectors (Your browser is basically hijacked and sent to the author's sponsor's websites, often for illegal items)
• Spam (a major space and time wasting issue at best, a portal for unwanted illegal material and further Malware at worst)