If I've just got everything in order, suddenly a contingency plan has to be put into operation! Ziggo had shut down our internet connection!!! Not because we're bad at paying... but because we're suspected of hacking others!
That must mean that we too have been hacked because we certainly do not spend our energy on that kind of nonsense. But where are you going to look? I installed the virus scanner recommended by Ziggo, but it also found nothing. I let that scanner run quietly in the background and then after some time I discovered that there was "something" on my computer that started a script every hour, at exactly 13 minutes before the hour, using the standard Windows Scripter (wscript.exe). Apparently, every time they ran a script that the scanner didn't trust...
Ziggo gave me some more insight into the complaint they had received. It turned out that from my IP address an attempt was made to get into other computers via SSH. The standard windows SSH was very accessible from wscript, so that was technically a possibility.
I now run the Ziggo scanner continuously and have also changed the name of SSH and other vulnerabilities. No, that's not 100% watertight, but it makes it just that little bit harder for the trojan robot that roams between my chips. In any case, Ziggo was satisfied with this, although they will keep an eye on me for the time being.

More than a whole day sacrificed to virus-writing idiots! And what have they achieved with it? Actually not a shred. Just have fun bullying people? Sad!!!