Help with Threat log SCAN: Host Sweep

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Help with Threat log SCAN: Host Sweep

L1 Bithead

I am looking for assistance interpreting a report that shows “SCAN Host sweep traffic” in my threat log. There are multiple internal sources scanning multiple destination IP addresses that I do not own. The daily number of scans detected from each source is between 2 and 10. The source machine rarely scans the same destination. Is this a low level attack trying to stay under the radar or is there an explanation that does not indicate a problem on my network? I appreciate any feedback.

Type: Scan
Name: SCAN: Host Sweep
From Zone: Inside
To Zone: Outside
Source address: Internal IP address owned by me
Destination Address: various external addresses not owned by me.
Port; 99% of the time 443. Occasionally port 80 or 22222


This screen shot show traffic during one time frame. I see various Source and Destination addresses.

sample date.PNG

This screen shot is filtered by destination address. This destination address is scanned various times from different Source addresses over the course of several days.

sample destination.PNG


L4 Transporter

Hello Hattracker,


1. Please check your zone protection setting, what is the threshold is set for it?

2. Have you applied for the zone protection on the internal/ trust interface? 

3, Please scan one of the clients with host-based IPS and AV, see if any ports are open. 



Himani Singh

L1 Bithead



I have been seeing the same and it is awful lot of traffic. I checked the destination IPs and most of them are Microsoft IPs in my case. However, I did notice some other IPs too which are flagged by some of the threat detection engines. 

The traffic has application 'not-applicable' which tells me there is no real data over the network but it more sort of probing with a packet or two.

I noticed most traffic going out over ports 443/80.


Have you done any packet captures?



I am sorry, no I do not have any packet captures from those events.  I did some digging at checked out a few machines. At that time I did not find any compromised machines.  It may be a good time to look at those threats again.

Yes, see if you can get some captures. I would do that myself too but I do not have the approval to do the captures on the target machines. I am running some on FW though as the time of this writing. Will let you now if find something interesting.

Found a lot of out-of-order and re-transmitted packets.

For me, some of the traffic is going to Microsoft servers with unrecognized text in XML and some other traffic going to some hosted servers which are apparently similar to the line of business. Did not find anything too concerning. 

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