We used to use Kaspersky, I found this happening to us:
Tracking URL Injection
We switched to FSecure, now called WithSecure.
I used Kaspersky for a while but after an upgrade I realized they had used NTFS Streams for storage and the new version went about removing it from millions of files and expected to take a month to do it! I ditched it and got a removal tool to remove the streams from some of my files. Took 50 hours to get rid of the crap. Never, ever touch that software again!
So sorry to hear about your troubles, Richard! 
I also use this for $11/mo it is unlimited automatic versioning backups a lot like MAC TimeCapsule
That is so unfortunate!
Currently I use Carbonite as backup. Had to configure it specifically to take app files, it tought it was a program. It has saved me on many occasions when an app/dct becomes corrupt, and it doubles as version history when I need to compare code in my apps.
Also I use Dropbox for documents, Clarion work and Clarion IDE. I have to turn off sync when working, because I get access denied when Dropbox tries to synchronize changes to clould.
I use Github for other development.
At home I have a stationary computer which is the “master” in my business, but using Dropbox and Github I have a laptop that is close to a clone of the master. I never keep these two computers in the same room, or leave overnight without taking my laptop with me.
All for a good night’s sleep.
That no different to a country’s own intelligence services, setting up a business which logs and bids on adverts based on the tracking data sent to advertising auctions for online adverts.
Just like the security services can claim to have a genuine reason for tracking people using online advertising auctions, Kaspersky might also have one. And in some respects its no different to tracking people using the free adblockers which download various block lists from github…
Seems like a sensible way, but one of many, to verify the file, it might even have speeded up their AV scan. The reason I say this, is just build a process to hash every file on your own hard drive, it will take ages, months even if using a “stronger” hash and have a terrabyte sized hard drive, and everyone will know AV scans from all AV companies dont take that long to scan a drive…
It could of also helped with file recovery, but that would have depended on what exactly Kaspersky were storing in their file stream.
Did you ever find out what they stored in their file stream?
I caught dropbox once scanning folders it was not setup to scan, so that came off straight away.
As for the rest, luxuries I cant afford after being done over by employees of the state and been made homeless and dependant on UC… but thats a long story! 
Yeah, back then you could open the additional streams using notepad and other software. It was benign information. The problem was that it was added to EVERY single file on this machine and I had millions of files on it - images, code, backups, etc. When Kaspersky came out with a new version it went on to REMOVE the extra stream, and estimated the time to do the “upgrade” at about 70hrs. Took me quite a whiel to figure out what the heck it was doing - ADS was not well known feature of NTFS at the time (this is like 2005-ish) Problem was that it ate up almost all the CPU of the machine and it became unusable. I removed Kaspersky and found software that could do this that was much easier on the CPU and I could pick what files I wanted so I let it run over a weekend and it updated about 60% of the files.