For v6 and v7 sites

gistfile1.txt

using System.Web.Routing;
using Umbraco.Core;

namespace RemoveRoutes
{
    public class RemoveRoutesStartupHandler : ApplicationEventHandler
    {
        protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            // Reference: https://github.com/umbraco/Umbraco-CMS/issues/5206
            // Reference: https://shazwazza.com/post/need-to-remove-an-auto-routed-controller-in-umbraco/

            // Note: RouteTable needs System.Web.dll
            RouteTable.Routes.Remove(RouteTable.Routes["umbraco-surface-UmbRegister"]);
            RouteTable.Routes.Remove(RouteTable.Routes["umbraco-surface-UmbProfile"]);
            RouteTable.Routes.Remove(RouteTable.Routes["umbraco-surface-UmbLogin"]);
            RouteTable.Routes.Remove(RouteTable.Routes["umbraco-surface-UmbLoginStatus"]);
            RouteTable.Routes.Remove(RouteTable.Routes["umbraco-api-Tags"]);
        }
    }
}

@bobi33 It has to stay in place.. it's the only thing protecting you if you do not upgrade to the latest version of Umbraco,