Since installing Norton Security on my mac (ElCap 10.11.5), I wake up in the morning to ALL internet activity being blocked... No messages, no indication of a threat - just no response from the net.
I discovered that disabling the firewall clears things up immediately. And, that afterwards, re-enabling the firewall sees no ill effects for the rest of the day... However, the next morning... Blocked again.
I have done nothing to whatever default settings are in the firewall section... I figure that as long as it doesn't stop me from doing what I do... then I don't need to understand or edit it.
Oh. And, no other security programs have ever been used with any of my macs. So, there are no residual bits running around the system.
This has become irritating enough that I am considering just trashing the whole business. I subscribed because of my PCs anyway. I thought that any benefit to my herd of Macs would be a plus... So, far it's not looking good.