Surreptitiously means:
* Done, made, or acquired in a secret or stealthy way
* Done without attracting attention
* Acting in a clandestine manner
For example:
* "The thief surreptitiously slipped the necklace into his pocket."
* "She surreptitiously checked her phone during the meeting."
* "The spy surreptitiously gathered information from the enemy's headquarters."