Hi parmour2,
You could read this avast technical message as follows: “In fact it says: Users in your own network environment could be able to alter some settings, when you have UPnP not disabled and they have info about the mem settings of your router”.
Check here: https://www.grc.com/su/upnp-rejected.htm
Hopefully you get
THE EQUIPMENT AT THE TARGET IP ADDRESS
ACTIVELY REJECTED OUR UPnP PROBES!
when not …
then disable with Unplug 'n Pray:
https://www.grc.com/files/unpnp.exe
polonus (volunteer website security analyst and website error-hunter)
For others to read: https://routersecurity.org/bugs.php