A staff member at HMP Liverpool was arrested as part of a probe into corruption in prisons.
Members of the Titan regional organised crime unit detained the woman at the Walton jail on Thursday and took her into a police station on Merseyside.
The 25-year-old was later released but remains under investigation after being arrested on suspicion of misconduct and intentionally encouraging the commission of offence.
Detective Sergeant John Davies, from Titan’s Prison Investigation Unit, said: “This arrest is part of an ongoing investigation conducted by the North West Regional Organised Crime Unit Titan Prison Corruption Unit to tackle the threat posed by corruption within prisons in the North West of England.
“We would like to make it clear to the small but determined number of prison staff who are involved in corruption that we will look at every opportunity available to us and the Prison Service to disrupt and arrest those involved.”