Hi Jepper, thank you for returning to this thread.
Sincerest apologies again for any frustration caused by the letter, we have fed back internally your concerns regarding the wording.
Our systems are able to identify an attack, however there is limited detail on what has triggered this. An attack can take place across any device on your network, and multiple things can trigger the system, including Viruses, software and dodgy apps which can hide on your devices. Anything that can send background ping to the network has the ability to trigger the alarm system.
As we would not be able to keep a log of every piece of software or app installed across all pieces of equipment on your network we would be unable to advise of exactly what triggered the system. We are just advised of a vulnerability on a device on your network, which we can then report to you.
The letter is sent from an automated system with the intention of protecting your network, devices and service. As mentioned in the last response from Kath above as long as you have followed the advice in the letter there should be no cause for concern.
You mentioned in an earlier post you have performed all steps advised in the letter, thanks again for confirming this!
If there is anything further that you would like our advice or support with please let us know.
All the best.