Sorry to hear about this.
Yes, if I had to guess, I'd guess that the user in question inadvertently installed a product called "Browser Safeguard" which is likely now bundled with a variety of other freeware applications as the primary Browser Safeguard installer is now blocked as "Unwanted software" by Microsoft's SmartScreen service and other security products. Browser Safeguard does indeed ILMerge a pre-Telerik version of FiddlerCore.dll into its primary assembly.
I've asked our legal team to look into this subject.
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