Account stealing is the act of stealing someones account by means of password scamming. It is considered by many to be a great source of lulz. This may be done in many ways. For example:
Scammer: Did u no that Jagex censors ur pass? Look: ********.
Victim: Reely? password
Scammer: Lol noob
Scammer logs out. Victim reports Scammer for password scamming.
Scammer (username is Jagexmemfind): Hello, V1ct1m. You have been selected for a free membership!
Victim (username is V1ct1m): Omg! Wow!
Scammer: Simply tell us your password and we can give you your free 18 months of membership!
Victim: Kk. Its password.
Scammer: Good. Now, log out and, in 15 minutes, you will have your free membership!
Victim logs out. Using another computer, Scammer logs into Victim's account and changes Victim's account password and recovery questions.
Victim tries to log in 15 minutes later. He learns that the Scammer has stolen his account and changed both his recovery questions AND password.