The network found out about the breach on June 22, and reset the PIN codes for all the affected accounts on June 25. In a statement to CNET Samsung said that the attempts used Sprint login details that "were not retrieved from Samsung." The telephone manufacturer has also thrown out several "measures" to reduce the possibility of future violations.
We have asked Sprint for more information, including when it is agreed that the breach occurred, number of affected users, and whether or not the account data was changed or used. The access through Samsung's portal suggests that the scale was limited (it's not the same as attacking Sprint directly). Anyway, it's not really what the network would probably report ̵