If it has no noticeable effect - my life is completely identical - it's hard for me to see it as something negative. If something has absolutely zero effect on my life whatsoever - not even a single advert on my screen - calling it a virus or malware seems unwarranted.

I suppose if my personal data was somehow used to damage someone else, that would warrant calling it malware.

Your stolen personal data could be used to empty your bank account or to commit a crime in your name which could cause permanent damage to your reputation, even if you were exonerated.

That sounds like something I would notice, and is thus outside the scope of this discussion.