I've been thinking that something like a shadow ban could be useful in these situations , and a few others. It seems most of these bots are using the same phrases without even changing a character. They've been doing this for a few days now. I'm sure mitchell could hook up his bot to automatically flag these phrases or report them automatically so there's a little bit of human interpretation to avoid any issues. Then if they feel the account is guilty of posting, and then deleting it's responses in hopes of bumping the topic it could get shadow banned.
Meaning they would see it as if they were posting their message, and deleting it. But, in reality no one else sees it. They are obviously running automated systems so probably wouldn't even realize. Even, if they did it would only take a little manual observation to determine their new sets of phrases, and add them to Mitchells bot.
I've noticed the example above posted by the exact same person for a few days now. "lastlinger". In fact just posted once again. I think this confirms that there aren't to many newly registered accounts doing this, and they are simply reusing their current accounts. Banning these members would likely result in them registering a new account, and starting over. Although, shadow banning could make it more difficult for them to tell.
I think this should be enforced for everybody on this forum.
Lots of hacked accounts are deleting their history, shills are deleting proofs after the
scam ICO has finished and many more....
I'm active on another forum where you can't edit your posts after 1 hour nor can you delete them, and it's pretty funny especially in the politics section to look at the users history and then rub it in their face

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This wouldn't really help the situation that the OP is about though. As they aren't waiting for a hour to pass, and are simply just deleting them after a few seconds have passed.