Simple Medium Credit Box

Simple Medium Credit Box is a premium class 2 lockbox. Upon use, these boxes award credit 325-497.

Source
Simple Medium Credit Boxs can be obtained through the Crew Skill Slicing. They can be harvested from Coded Safe Boxes on Balmorra (Empire) and Taris (Republic), which requires level 55 Slicing, or from level 17-24 Slicing missions.