/diy/ - Do It Yourself

Noob electrical question. I just moved into an old house and was told that it doesn't any grounded outlets (most are still 2 prong). At some point, several of the outlets were converted to three prong. I have plugged a simple ground tester into them and get nothing. It is a very basic tester. If it lights up, there is a ground. No light, no ground. In the kitchen and the bathroom, there are GFCI outlets. When I plug the tester into them it shows them as having a ground. Would the outlet being GFCI cause my tester to show them as having a ground?