.minecraft folder exploit

Hello. Recently i copied my .minecraft folder from /AppData/Roaming to my second hard drive because i had to refresh my Windows and i didn't want to lose my Minecraft versions, screenshots, and saves. On the new system i installed Minecraft Launcher from official website and i copied back my .minecraft folder to /AppData/Roaming then i opened the Launcher and i didn't had to login to proceed to launch Minecraft. With that, a hacker can just copy the folder to his computer and launch the game using someone's account without logging to Launcher. I really apreciate any respond or fix. Thank you

• Krzysztof "Winter" Okonowski