Yesterday I have analyzed what happened and why.
Everything began on Friday, when I plugged my USB Flash drive into the PC of my colleague. He had a malware on PC. It infected my flash drive. My flash drive infected my pc, pc of my wife and pc of my mother in law (we have visited her yesterday).
I though what could I do to remove the malware as soon as possible, before it turned into a terrible monster like ransomware etc. One good idea crossed my mind. I could restore windows to a state before the event. So I did it on the PC of my wife and I think it helped. I tested it with a Flash Drive and the drive was not infected anymore. I hope it will stay clean. I will keep my eye on it.
Now I want to do same on my pc and the pc of my mother in law.
@Pondus thank you for recommending Flash Drive guard MCShield. It is a great software. will install it everywhere.