Office 365 Automatic Download Sandboxed - COMODO issue

Hi All,

Wanted to provide a general update - COMODO blocked certain files from a Sunday 23rd July automatic update which caused O365 to not update correctly. This stopped my colleagues and I from accessing O365 software and files, as our user account was no longer connected to the software. This caused significant issues, delays and lost time for our office, as we’ve had to work from our personal computers until the problem could be fixed.

We only found the root cause after two days of trial and error with a level 2 Telstra support specialist.

We fixed the problem by re-adding Microsoft Suite as “Trusted Applications”, uninstalling and reinstalling the Microsoft suite.

We’re unsure if this was ultimately a Microsoft problem, or a COMODO problem, however wanted to post it here for reference in case the software engineers hadn’t encountered this scenario recently.

Have been happy with COMODO services other than this.


Hi NickSydney,
May you please go to Log section from main interface via “View Logs” and save “Executed Applications” log and provide that here or via personal message?


We have investigated further, it seems Microsoft has released an update to Office, where files are digitally signed using root certificate that is not in trusted root certificate list.

Please have a look at enclosed snap, showing the problem.

This is causing digital certificate based validation failing as certificate chain can not be trusted and thus making trusted vendor list having no impact.

We are ensuring that MS Office files gets whitelisted by sign and safe signs available in cloud in addition to being released in CIS as part of AV updates.


Then, would adding the Root Certificate Authority of the updated MS files to the Trusted Root Certificates of Windows solve this issue?


Technically yes, try.