The theory is that not responding to "ping" tells the hacker that there is nothing interesting at that IP address.
In practice, hackers don't care. I would help a friend, from time to time. I set his equipment up, per his request, to not respond to "ping". By contrast, in order to participate in a DSLR group monitor, my own equipment responds to "ping".
In comparing the two system logs, the only difference was that I got more attempts on port 25 than he did. Otherwise the logs looked very similar.
Nothing about responding to "ping" makes port 25, "interesting"; but having a published MX record will guaranty attempts to connect via port 25.
Here is my group monitor:
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/te ··· 41472000
