surreptitious
/ˌsər-əp-ˈti-shəs/
adjective
done, made, or acquired by stealth : clandestine
acting or doing something clandestinely : stealthy
secret covert stealthy furtive clandestine surreptitious underhanded mean done without attracting observation. secret implies concealment on any grounds for any motive. covert stresses the fact of not being open or declared.