The messages are sent to those who like, respond to, or comment on a post that contains false claims about the corona virus on Facebook. This applies to posts that are then removed by Facebook's moderators.
The news agency AP writes that the effort is never seen before and that Facebook is now changing its algorithms, in the face of stricter rules and fact checks.
"During this crisis, it is important that you get accurate and relevant information," Facebook CEO Mark Zuckerberg writes on Facebook.