Windows 10 File Corruption Causing Unprintable Bytes in Various File Types: Possible Virus?

[PickyBiker]

Something is corrupting files on my computer by putting 3 unprintable bytes at the beginning of some files. The characters are unprintable and the hex values are always the same, EF, BB, and BF

There are over two hundred files like this on my system. Most of the affected files have the following extensions: .vb or .js with a few other types as well:
.scad
.h
.pyproj
.sln
.json
.sln

It is the .json file that raised the problem for me. When these characters are in the file, it causes the json file utilities to fail.

I suspect it is a virus but a few different antivirus programs avg, kaspersky, and adaware find nothing.

Ideas?

 

[patcooke]

This article explains what it is:

Byte order mark - Wikipedia

There is a brief discussion of it here:

EF BB BF prepended - .NET Framework

 

[PickyBiker]

Thank you. At least it's not something bad. I will just detect this and strip them out in my program before I do anything with json files.

Don't know how they suddenly started occurring in json files, but I suspect it was because I was creating them with notepad.