Youtube has updated its the rules for what is not allowed on YouTube to include content that encourages violence or dangerous activities.

Currently, Youtube's Community Guidelines, which not only apply to videos but all content, including comments, thumbnails, links, posts, live chat, etc., do not
allow pornography, incitement to violence, harassment, or hate speech in any form on YouTube. Youtube relies on a combination of people and technology to flag inappropriate content and enforce these guidelines.

The updated rules do not allow dangerous challenges and pranks - content that encourages violence or dangerous activities that may result in serious physical harm, distress or death. "We’ve updated our external guidelines to make it clear that we prohibit challenges presenting a risk of serious danger or death, and pranks that make victims believe they’re in serious physical danger, or cause children to experience severe emotional distress," Youtube Community Manager said.

In addition, Youtube said that all custom thumbnail images must follow its Community Guidelines. Selecting a thumbnail that egregiously violate policies (e.g., containing pornography or graphic violence) will now result in a Community Guidelines strike, even if the video does not violate Youtube's policies. Multiple strikes will result in the loss of a channel’s custom thumbnail privileges and three strikes in 90 days will result in account termination.

Last but not least, all external sites linked from YouTube must follow the service's Community Guidelines. Adding links to external sites that egregiously violate Youtube's policies (eg., pornography, malware, or spam) will now result in a Community Guidelines strike. Receiving three strikes in 90 days will result in account termination.

Youtube said that in the following two months, content that violates the company's Community Guidelines related to custom thumbnails, external links, challenges, and pranks will be removed but the channel will not receive a strike. Content that was posted prior to these enforcement updates may be removed, but will not receive a strike.