The star detailed the incident during Sunday's (October 13) episode of "Keeping Up with the Kardashians", telling her sister Khloe Kardashian what happened after she and her staff start noticing money missing and iPads disappearing.
They quickly realised the culprit was someone in the house, with the mother-of three explaining: "This lady stole $700 (£556) out of my wallet, then she stole $4,500 (£3,575) out of Scott's."
"Then my security, who's here today, just said he's seen her two times with her flashlight on in the office."
Kourtney later revealed the unnamed woman is at the house, adding that one of her assistants "just pieced it together," and the woman is looking at her texts and has "hacked everything."
As the pair run down to confront the perpetrator, they see a car screech off and begin angrily asking her security staff why the woman was allowed to leave.
However, Kourtney is more focussed on taking immediate action, saying: "We need to change the iTunes password, right now."
"We need to debug the house and I want to take every device and unconnect it from my phone," she continued. "And next time, we've learned a huge lesson. They cannot step foot in here for an interview without us having their social, name, and address."
As the episode ends, she still hasn't caught the woman, but insists she's more focused on "moving on", explaining: "I obviously can't change what happened, but like anything in life, I believe that this is a big learning lesson... I just want to start fresh and get this bad energy out."