For the simple server-crash (the one that doesn’t take down all of your servers at once), what’s crashing the server isn’t the spamming of the welds. It’s the deletion of the welds. A smart exploiter who isn’t simply using scripts released online, knows this, and it’s up to roblox to fix. Even if you put up some sort of way to kick players or delete the welds, it wouldn’t do anything. The real problem is the replication.
Even if you kick the player, that’s still not fixing the problem of deleting the welds. As you know, you can’t delete an instance the exact moment it’s created, even via. ChildAdded, it’ll simply error, saying that something tried to parent the Instance to NULL as it was being parented to wherever. Thus, the welds are forcibly created, there is no getting around it. And even if you kick them, kicking them deletes all of the welds, crashing the server anyways, all an exploiter needs to do is instead of loop-spamming instance creation, create the instances perfectly simultaneously, and let the server frantically handle attempting to destroy all of the instances.
They simply create the 60,000 welds, then let the script run and drop them in the void/ or get kicked by the game, and no matter what happens, the welds are deleted and this crashes the server. The only solution is through roblox preventing its replication.
For the one crashing all of your servers are once, I can guarantee it isn’t a backdoor though, it’s been used on Stickmasterluke’s ‘Fencing’, which hasn’t been updated in years, and hasn’t been worked on by anyone else. Other than that, can’t give any more input on this matter.