Difference between virus, worm and Trojans

VIRUS:

Virus are the unwanted programs which infect other files, commonly .exe. They multiply with these exe files and modify or delete datas.

WORMS:
They are like virus but they donot modify or delete any data. They consum a lot of resources like your hard disk space by multiplying.

TROJANS:
They are like virus but sometimes very dangerous as they are often associated with RAT(Remote Access Trojan) or keyloggers. Initially you dont know that a trojan is running on your computer. They can send Keyloggs, Pictures and every activity associated with your computer as per their settings. They are generally contained within a legitimate program that user cannot understand that it is having trojan.