On practically any server that uses a mysql database to link two or more servers you can use -multirun to log into both servers and manipulate things by overwriting your data with a second instance of Garry’s Mod.
There is no convar I or anyone I’ve asked knows of that can disallow people to use multirun on your servers.
There is no easy way to fix this that doesn’t require most mysql based addons to be heavily modified or recoded.
**1. Join two linked DarkRP servers, drop all your money on server A, drop $1 on server B, reconnect to server A, pickup your dropped money and you have now duped your wallet. See here.
2. Join two linked servers with pointshop, spend all your points on both servers effectively doubling your points. Even though it is done what most would call the proper way it is still vulnerable.
KingofBeast and I made a quick addon that will kick multirun accounts (Hopefully Rubat or Willox will add a convar/hook in the future so hacky fixes like this aren’t needed):