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I've bought a KM (keyboard-mouse) link cable. When you connect 2 PCs with this cable, you can use either PCs with a single mouse/keyboard. Also you can make data transfer by just drag&drop.

This cable comes with an embedded software that does all these KVM features. The problem is, that my antivirus, Avira, detects is as Trojan. (However when I submitted the file to VirusTotal, this seems like false-positive)

This makes me worry because if this is a keylogger malware my credit card information and every single thing I type will be sent to the hacker.

So, I want to add the process to Windows Firewall so that it can never connect to the internet. However, since this thing communicates through USB cable between 2 PCs, it should still be able to transfer data through USB port.

How do I achieve this? When I create an outbound rule on Windows Defender Firewall with Advanced Security, it blocks all connections so the feature is totally blocked.

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  • windows firewall can only add programs,ports in outbound rules. You can specify the program used and add into the outbound rule.
    – Gloria Gu
    Jan 18, 2021 at 8:59
  • If the data transfer really goes directly through the USB cable than the KM switch must register another USB device type because data transfer via HID (mouse/keyboard) profile would be a bit slow. Most likely the KM emulates an Ethernet cable which effectively means that your non-Internet PV would then be indirectly connected to the Internet.
    – Robert
    Jan 18, 2021 at 16:56

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Firewall doesn't affect USB connections. Apparently this software communicates over existing network, or the hardware emulates a USB network adapter used by the software.

You have to add a firewall exception to allow communication over the emulated network interface or on the port used by the software. You can find the port number either by looking at ports opened by the executable or by sniffing network traffic.

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  • Is that so? This definitely communicates via USB so it must be some kind of an emulation. Looking at the ports opened by the exe doesn't seem easy.... or is it?
    – user8491363
    Jan 19, 2021 at 2:31
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    @user8491363 netstat -a -b -n
    – gronostaj
    Jan 19, 2021 at 6:41
  • The list is seriously long but I guess it's the only way then.
    – user8491363
    Jan 19, 2021 at 7:03
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I have used those cables in the past when moving someone into a new machine. It basically links two pc's via a special usb cable and some software. This communication occurs over the custom usb cable and the firewall is not involved in this action. If you want to prevent the machine from communicating with the internet then go into device manager and disable the network card. Goto Device Manager, expand networking, right click on the network card and select disable.

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    Then you're completely shutting down the internet. I only want to prevent the software that came with the cable from connecting to the internet, so that no information can be sent via that process.
    – user8491363
    Jan 19, 2021 at 2:29
  • Simple then, go into the firewall and specify that that program is to be blocked from getting out. Hackers do it all the time. Go to outbound rules and create a rule, it will give you an opportunity to select the program by name, and specify to block. very common task.
    – Larryc
    Jan 20, 2021 at 17:46
  • go to the firewall, advanced settings, select outbound rules. right-click, select new rule. follow the wizard, PROGRAM, browse to the executable, etc...BLOCK etc...
    – Larryc
    Jan 20, 2021 at 17:53
  • that's what I did when I did that keyboard-mouse communication with the other PC stopped, implicating that the firewall blocked the connection between the 2 PCs. I was looking for a specific firewall setting to allow USB communication but not internet communication. That's what this question was all about.
    – user8491363
    Jan 21, 2021 at 8:56
  • OK then, the usb cable came with software, When installed it creates its own rule(s) to allow the usb connection. Your firewall rule overrides it. So next step depends on the software installed. Also notice under Connection Security Rules you can setup device to device connections but this would apply to network communications not usb. But you can restrict all communications between the two devices ONLY. So the option is there, be aware of it. And one more option, block the device at the router -no outbound packets allowed. This might be your best option.
    – Larryc
    Jan 22, 2021 at 12:13

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