How Bluetooth Works
Common bluetooth connection is equipped with simple radio transceiver and contains both software and hardware parts. The hardware part is equipped with antenna that is getting a signal and then passing it to the software part, that in its turn interprets the signal. After the software part spells out incoming signal, it sends the signal out to the other devices, so they can receive the information in proper format. One bluetooth adapter is able to connect up to 7 devices at the same time. When your Mac is connected to the printer, headsets and other gadgets via wireless connection, it doesn't mean that the bluetooth connection is working real-time. Devices are only connected in case of “request - response”, so it’s pretty difficult to connect 7 devices at the same time.
At the same time the growth of wireless connection via bluetooth is boosting potential hacker attacks on it. Imagine how many wireless connected devices are in every office, from keyboard, printer, mouse to wireless speakers and headsets. More and more devices are switching to a wireless connection.
As for security of the Bluetooth connection in the Mac OS, this question now is not quite understandable. Starting from Mac OS X Yosemite, a lot of security features for bluetooth connection were abolished, such as encryption or managing of visibility. Let’s see how to secure bluetooth connection on your Mac.
1) If you do not use Magic mouse or Magic keyboard, you may just turn off your bluetooth connection, so your Mac will not be visible for other devices.
Go to System Preferences > Bluetooth > Turn Bluetooth Off.
2) Since Mac OS Yosemite has been launched, Apple uses the “Handoff” technology. This technology allows to synchronize all devices with the same Apple ID via bluetooth, making it possible to start working on iPad and finish the work on a Mac. For example, you start writing an email on iPad and then your iPad transfers all details to your Mac where the same web page or app will be opened. The security of such kind of connection is a big question. You may disable this feature in a few clicks.
Go to System Preferences > General > and then deselect Allow Handoff between this Mac and your iCloud devices.
3) In El Capitan you can set up Bluetooth Sharing features. This option allows other devices to find your Mac and connect for sharing items.
Go to System Preferences > Sharing > select Bluetooth Sharing. On the right side of the window you will see the Bluetooth Sharing preferences, such as how would your Mac react when receiving items or how to react when other devices browse your Mac. Here also you can choose the folder for accepted items and the folder that other devices would be able to browse.