This reminds me of what my mom asked me after hearing about bitcoin for the first time:

"Well, if the the money is stored on your computer, doesn't that mean that anyone who controls your computer controls the money?" (Paraphrasing, that was the gist of it.)

To which I gave an emphatic yes. I also pointed out that if you store your credit card details on your computer, whoever controls your computer controls your credit card. Though at least with that theres some amount of insurance against fraud.