furtive - sneaky
The word ‘furtive’ can express a person conducting themselves in a clandestine and often dishonest manner, or actions that are characterized by secrecy and immorality. The term implies suspicious behaviour; as if the person in question is plotting or trying to hide something. Typically used in a negative context.
I cast a furtive glance around the shop to make sure nobody was looking before I stole the money from the cash register.
A cabal within the company were working furtively to siphon funds into their offshore bank accounts before being exposed by a whistleblower.
I don’t want people to know that an investigation is taking place, so you must go about your business with a degree of furtiveness.