That is bizarre. I assume you are using a newish version of Frutiger here. It's not old an Postscript font, is it?
You might want to try changing font embedding percentage - I've fixed similar problems by trying to avoid subsetting of fonts by setting embed percentage to 1%. But, really, that is one of those magical-thinking fixes, like toggling Tagged PDF state at export.
How are you making this PDF? Is Distiller involved, or are you exporting?
Can you share the PDF and/or INDD via Dropbox? (I'm only asking because I honestly have no idea why this is happening to you, and it's often easier for me to figure out this kind of thing by experimentation instead of by question/answer).
Virus? No, I am pretty sure that it's not any kind malware.
My gut feeling is that it is a combination of things, especially if it only happened once in one file. Happened to me all the time in the other direction (making Chinese PDFs with English InDesign CS3) that old Postscript fonts would drop a character if they appeared in a file with something in, say, one of the more obscure GB chraracter sets that was remapped to a CID encoding upon export to PDF.
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