It's an auto checker Nexon has. Everytime you log in the IP is logged of course. But once you log in with a different IP a lot of times in a day the account is automatically locked/banned/suspended.. Most of Nexon is an auto thing.
Guys , if you login an account over 50 times a day it locks your account. If they see your account on 5 or more IP's they will ban you. Greatfullded shares accounts with his brother but there on same IP :\