Whenever we get news about viruses some are referred as viruses and some are referred as worms. Therefore many do not know the difference between virus and worm.
Viruses are computer programs that multiply themselves. These programs will get embedded into other programs and hide inside them. Some viruses even enter into Operating Systems and function as per their commands. But viruses cannot spread from one computer to another computer unless it is attached purposely in an email and send to another computer manually.
Worms are also computer programs that multiply themselves. But instead of multiplying and spreading in the same computer they spread between one computer to another computer. The whole system is affected by the worm. Therefore the computer's performance is affected and slows down. Worm computer will be in the network and destroy the memory. It will identify other computers in the network and spread to them. To whichever computer it goes it will access the address book in that computer and send itself to all the addresses.
Therefore you can say that Worms are created for the purpose of spreading between computers and Viruses are programmed to stay and multiply in the same computer.
Worms take control of your computer while viruses delete files from your computer.
In both cases, it destroys your computer. So it is a good practice to protect your computer from them.