Recently one of these messages started to pop-up on the news website I frequent (and where I pay for a subscription!):
You are seeing this message because ad or script blocking software is interfering with this page. Disable any ad or script blocking software, then reload this page.
It is difficult to block this element in uBlock by standard picker as the div element changes its ID on every page load and the ID consists of random characters such as “572onu654ny6”.
Go to uBlock dashboard (rightmost icon) -> My filters and enter this custom filter (change example.com for the domain you see this warning on):
Also see a discussion over at BoingBoing.