Many Flight Simulator fans who fly connected to air traffic networks (like VATSIM) report that their security suite (firewall/antivirus) prevents them from seeing other users' aircraft. No one seems to understand the root cause. There are many "cargo cult" solutions, mostly involving uninstalling the security suite. Just disabling it, or its components, doesn't solve the problem. I've confirmed this for ESS. I have to completely uninstall it to see the simulated air traffic. I've done more research and data collection, and the problem seems to be with the communication between the Flight Simulator software (mine is Microsoft 2004, a.k.a. fs9.exe) and the Microsoft DirectPlay8 software (dpnsvr.exe), on the same machine. I run a program called SquawkBox 3 inside fs9.exe. SquawkBox manages the connection to the air traffic servers, and I can confirm that at least some data about other aircraft are getting through the firewall. They're just not displaying. I believe that the display is handled via DirectPlay8, on ports 23456 and 23457. I've run ESS in interactive mode and verified that communications are being requested on these ports, and that ESS considers them to be within the Local Zone. The relevant netstat lines are (obtained with ESS uninstalled, and air traffic visible) are: UDP 192.168.1.101:23457 *:* [fs9.exe] UDP [2001:0:4137:9e50:3ca6:3a41:3f57:fe9a]:23457 *:* [fs9.exe] UDP [fe80::5efe:192.168.1.101%34]:23457 *:* [fs9.exe] UDP [fe80::3ca6:3a41:3f57:fe9a%8]:23457 *:* [fs9.exe] UDP [fe80::9cad:95bf:3c3d:fc1b%10]:23457 *:* [fs9.exe] I've also verified that the ESET controller (ekrn.exe) does not use these ports, or any other ports used by any Flight Sim or air traffic network component, so I don't believe that it's a port conflict. Somehow, ESS, even with the firewall turned off, appears interfering with this traffic within the local zone, and I'm completely stumped as to the root cause. I've done lots of things with ESS rule sets (firewall) and excludes (antivirus) and have been unsuccessful. ESS is a fine product, and it frustrates me no end that I would have to completely uninstall it to get my own laptop (Dell E1505, Vista) to talk to itself. If any ESET support engineers are reading this, and you would like me to collect some additional data, I will be happy to. What about that UDP traffic in the local zone could ESS be concerned about, even with the firewall turned off?