Someone logged into a cracked server using a cracked launcher by using my username.

Someone I know recently gained access to a cracked server using my account. I want to write this so that both employees and players alike can see this and prevent anything like this happening to them.

Yesterday a friend used a cracked launcher (sk launcher) to gain access to my account by using my username. Upon interrogation he said that since my username is attached to my UUID, upon logging into sk-launcher it will share the same information as my actual account, skins and everything. He was able to log into our private server on which we play together, using my account. After I checked log (we use aternos) I found that he had somehow logged in using my account.

If more people started using cracked launchers to gain access into cracked servers using other people's usernames, I can see nothing but chaos in the future. Please resolve this issue, as it ruins the fun for actual players who paid for their account.