You have Office 2016 installed, have ADFS and ADAL authentication mode and are accessing a SharePoint online web page. When you mouse over the presence indicators or try to look at contact info you are continually prompted to enter credentials. This may only impact remote users.
This is a product limitation.
Disable the NameCtrl Class IE-addon
Microsoft wants to address this issue, but the changes required are too big for a hotfix. This scenario will be addressed sometime in the future.