Judas/judas:
(plural: ‘Judases‘/judases‘; for the right pronunciation, please click here)

Biblical Judas (R) betraying Jesus
a person who helps the enemies of his/her friends in order to harm his/her own friends, usually for some personal benefit;
a traitor — a person who cheats his own people or country (named after a character in the Bible, a disciple of Jesus Christ, who helped Roman soldiers to arrest and kill Jesus for money),

modern day judas (The Pope’s butler who leaked important Papal documents)
The investigating committee of the company suspects that there is a Judas in the company who is selling the secrets of our company to our rival companies., i.e. the committee suspects that some employee in the company is giving out important information to the other companies.
It’s commonplace in politics to find a number of Judases who betray their own party by helping opposition parties while still enjoying the benefits and privileges from their own party.
