Let me see if I can find a word for someone fitting your description:

T-R-A-I-T-O-R

traitor >noun a person who betrays their country, a cause, etc.
-DERIVATIVES traitorous >adjective.
-ORIGIN Old French traitour, from Latin tradere 'hand over'.

B-E-T-R-A-Y-E-R

betray >verb 1 act treacherously towards (a person, country, etc.) by revealing information to or otherwise aiding an enemy. 2 be disloyal to. 3 unintentionally reveal; be evidence of.
-DERIVATIVES betrayal >noun betrayer >noun.
-ORIGIN from Old French trair, from Latin tradere 'hand over'.

Betrayer - (n) one who reveals confidential information in return for money, a person who says one thing and does another.

S-C-O-U-N-D-R-E-L

scoundrel >noun a dishonest or unscrupulous person.

I found three!