This is an important step in diagnosing a hard drive that is in trouble. I have observed that sometimes, after viruses have been eliminated from a drive, they will test as "Failing", with the message to retrieve as files from the drive and then replace it. I think that one or more viruses are capable of writing a value to a drive that is neither a "0" or "1". Because of this, the drive appears to be failing. On these drives running a low level format will correct the problem. Note that the advice to retrieve files from the drive still applies. I have found that this works on about 50% of the drives that show symptoms of bad sectors, especially in drives less than three years old.
The Maxtor software works on all drives for testing purposes.