CIS has received many reports from Macintosh users about the annoying yellow screen for no good reason while using Bronco Wireless. Windows and Macintosh computers will both occasionally receive this screen and this is by design but Macintosh users sometimes experience this screen without an obvious cause. The yellow screen is a required security component on our network. While it may cause some frustration when you encounter it, not having it would be much worse.

What is the yellow STOP screen? (when working as intended)

SUNY Delhi uses a tool on the wireless network to prevent the spread of viruses and other malware that can steal data, damage computers, and disrupt services. The way it works is relatively simple but effective. Each computer connected is monitored for the number of outgoing connections it is making to the network. A normal healthy computer might open 20-60 connections open at one time. You may not be doing anywhere near that much stuff, but your computer is quietly communicating with the network in the background. This is normal. If your computer becomes infected with a virus, this number of open connections will usually skyrocket and hover at 500 or more while the virus attempts to spread itself or perform other malicious activity. When the network sees this unusual amount of traffic, you will be temporarily quarantined from the network to avoid spreading the virus. You can then clean the infection and when the computer is back to normal the quarantine will be lifted and you are back in business.

Why do I get it all the time on my Macintosh?

Apple does a very good job of creating consumer devices. Unfortunately in many cases, they do not operate well on larger networks. While this is starting to change, there is still work to be done. Macintosh uses a service called Bonjour on the network. Bonjour basically does what you would think it does by its name. It says "Hello" to the network. The idea is that if you have a bunch of Macintosh computers, they will all know each other on the network because they talk to one another through the Bonjour service. This makes it easy to share files and access printers and other devices on the network that also run Bonjour. This is all well and good on a personal network. The problem with the Bonjour service is that it generates a significantly larger amount of outgoing connections. Even when your machine is not being used, it is sitting there advertising its presence on the network. This additional traffic is quite similar to the traffic generated by a virus infected machine. The result is that you may get the yellow STOP screen for seemingly no reason at all. Even when the block is removed, chances are it will come back.

Can I stop this from happening?

Step 1:

The good news is that yes, you CAN stop this from happening.

For many users, simply enabling the built in firewall in Mac OS will do the trick. Click here for instructions on enabling the firewall. Be sure to follow the instructions for the version of Macintosh OSX that you are running

Step 2:

For other users, the problem persists after enabling the firewall. For these users, we have identified another way to stop this from happening. Essentially, this process will disable stop the bonjour service from advertising on the network.
*Warning:* This guide is not intended for beginners. It is detailed enough to follow step by step, but it is not for the faint of heart. To make this change you will be required to enter commands and work from within the terminal application on your Macintosh. If you are not comfortable with this, we recommend that you have someone who is comfortable working with the command line help you or take your computer (with this guide) to a professional computer repair facility to have this done.