You will need a wide-mouthed insulated flask (actually, a normal one will do, but you might have trouble getting the yoghurt out afterwards), a saucepan, some milk, and a small sample of the yoghurt you wish to pirate.
Warm the flask by filling it with freshly-boiled water.
Heat milk to just below boiling, then allow it to cool to about 40C. If you don’t have a thermometer, just let it cool to the point at which you can comfortably hold a (clean!) finger in the milk.
Mix in a spoonful of the source yoghurt—a whisk works well.
Empty the flask of boiling water, fill it with the milk and yoghurt mixture, and screw on the cap.
Leave the flask for six to eight hours; I prepare it before bed and it’s done by breakfast time.
Although this is an analogue process, there’s very little generational loss: you can use the second-generation yoghurt to inoculate the third, and so on yea unto the N+1th generation.
Incidentally, if you think describing this as ‘piracy’ is ridiculous (and it is), you should read about seed piracy.