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Explanation: As we don't have any context, and this is a log in name, where people are known to give freedom to their imagination, it could as well be the beginning of the sentence (אני בורג (קטן במערכת, which is the parallel to the English sentence I am a (little) cog in the wheel.
Alternatively, בורג is also a surname, Burg. There are several politicians in Israel (father and son) who answer that name. It would then mean 'I am (a) Burg', subject to check the person's surname.
The above answer I am a screw is a good guess too.