"If you fight fire with fire, you will get burned". - John Diggle Pandora is a memory stick created by Helix. It was given to Felicity Smoak to get information that can incriminate General J.G. Walker. He had framed John Diggle for murder and other crimes. Felicity had used Pandora so John Diggle would be released from prison.
Felicity started to use this device to get dirt on many people such as politicians, lawyers etc. Felicity started using this as a weapon and John said to her "Come on this isn't you". John also said "If you fight fire with fire, you will get burned". Felicity later uses John's quote when she decided to join Helix and continued to do similar things at the Helix base of operation which is how Adrian Chase was outed as 'The Throwing Star Killer' a.k.a Prometheus.