surreptitious
adjectiveObtained, done, or made by clandestine or stealthy means. synonym: secret.
Done by stealth, or without legitimate authority; made or produced fraudulently; characterized by concealment or underhand dealing; clandestine.
Acting in a crafty or stealthy way; guilty of appropriating secretly.
adjectiveDone or made by stealth, or without proper authority; made or introduced fraudulently; clandestine; stealthy.
adjectiveconducted with or marked by hidden aims or methods
adjectivemarked by quiet and caution and secrecy; taking pains to avoid being observed