LMS substituting fonts

Hello,
I've created some modules for a client. Fonts display fine on 360 Review and any computer I tested them. However, the client has published the SCORM files and now the fonts have been substituted by what seems like Times New Roman and characters are all misaligned. 
In the screenshots I received, it seems the client is using an old Explorer browser. Could it be the problem? 
Even the menu and next/previous buttons are using a weird font, which indicates it is not a problem of my using non-standard fonts.

Any help would be much appreciated.

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