I'm aware that there are other threads on this topic here, and I've read all of them. Most of them seem to relate to free or home-user versions of Avast, and that's not what I'm using. Also, the explanations offered by Avast people in those threads are general in nature. That isn't helpful to me.
Can anyone provide some specific and detailed explanation of what could possibly cause the specific behavior described below:
I am using Avast Business Pro with the on-Premise Console. Program 21.6.x
On Sunday morning September 5 (EDT, Eastern USA), the Avast client on a single Windows 7 workstation on my network issued three alerts of SMB:BruteForce, each precisely 30 minutes apart. The alerts reported that an IP4 address leased to a single iMac was attempting to connect to this workstation. This iMac only connects to my network via wireless, and it only has access to a separate VLAN that is configured only to provide internet connection sharing.
The iMac was unattended, and had been left in "sleep mode". However, the IP address is definitely leased to that device, and the lease doesn't expire until September 14--a week from now.
Therefore, this iMac should not have been able to even see any other workstation on my network. As I understand it, because it was on a separate internet-only VLAN, it should not have even been aware that it was ON a network.
So what specific set of circumstances could cause the exact behavior that I have described here?
Thanks very much for any specific--not generic--response.
[Edited Sep 8 2021 10:30 am EDT to correct an error (it was an iMac, not a Mac laptop) and to add that it was running at the time but in "sleep mode".]