We've recently seen a situation where users of Dynamics365 (a.k.a. CRM Online) are getting popups or redirects to an url such as:
With the support of Microsoft support we have been able to solve this issue by adding the following sites to the trusted sites of Internet Explorer:
And to remove the temporary files from Internet Explorer as well as the folder "%temp%".
Keith Cockerham has identified the guided learning path as the cause of this issue. Turning off this feature using another browser is another workaround for this issue, but keep in mind that obviously you cannot use the guided learning path feature in this scenario.