Note: if you only get this kick on a specific server then chances are a mischievous plugin developer is faking the message to prank/troll you. This is not allowed and the plugin can be reported, but you don't need to worry: it isn't possible for plugins to globally ban you.
Otherwise this means your Steam account was banned from Unturned by Valve Anti-Cheat (VAC). Please refer to this Steam support article: https://help.steampowered.com/en/faqs/view/647C-5CC1-7EA9-3C29