Give Spy Holodisk to authority in NCR

Detailed walkthrough
When in Vault 15, go to where Darion was standing and scan the computer right behind him. With a high enough Science skill, one can get the NCR spy holodisk. Take the holodisk to NCR, tell president Tandi about Khans having a spy within her government, she will realize that Feargus (the person in the Hall of Congress entrance room) is the traitor and tells him to give the disk to her aide Gunther.

Once given Gunther the disk, he will a reward of $4000. Afterwards, Feargus will promptly leave the republic after having been disgraced or executed for high treason (the holodisk's data can be transferred onto the Pip-Boy 2000).

Отдать диск шпиона властям НКР