Code masking

Code masking was a tactic used by pirates and privateers to stay one step ahead of law enforcement agencies. Pirates used a masking code modulator to interfere with a ship's transponder code. The modulator created a new transponder code, or at least one that was similar to that used by another ship. When active, the masked ship appeared to be another vessel of the same model.

Sources

• Pirates & Privateers (First mentioned)