A Whitehat hacker is an information security professional, who utilizes his hacking know-how for ethical purposes to e.g. support organizations to strengthen their cybersecurity competence. A blackhat hacker on the other side usually intends to perform criminal activities.
A worm is a type of malicious software which is able to replicate itself and spread to other IT-systems by e.g. using network connections. The difference to a virus is that a worm stays a separate entity and does not need to be attached or inserted to other files. Mostly worms do not cause direct damages as for example viruses do, however they can have strong negative effects on networks if they have a high bandwidth consumption.