You're catching on. Sealed indictments are sealed for the purpose of keeping what they contain secret. They usually come with gag orders. The gag order is put in place when or before the indictment is unsealed. No one, not even the accused, can talk about it, except with their legal council. The gag order remains in effect until a judge determines that it can be made public. A person who receives an indictment isn't necessarily held in custody. They can walk free until that time, but will be monitored and have restrictions imposed on their their movement and activities.