Formerly, it was only computers that got hacked, but today phones are becoming increasingly similar. There are programs that hackers can save to their computers at home which, combined with a Bluetooth antenna, can be used to get into other's stuff. However, this will only occur if people leave their Bluetooth connection on continually when traveling around during the day.
People can sometimes get onto other peoples' files through Bluetooth if you are negligent and leave the function on. With the Bluetooth antenna, the hacker can sit back and let their computer hacking program do all the hard work, whilst you are completely unaware that it is happening.
The computer program will automatically rip all sorts of content from your phone, including text messages, emails, contacts, images, video and even SIM card details. More pressingly, the hacker can even send corruption codes to your device, meaning that they can corrupt all files with remote access, essentially destroying your files without you even knowing the cause behind it.
So, always be careful to keep your Bluetooth and Wi-Fi connection off when you don't really need to use it, it can be the difference between having your stuff on your phone kept safe and being looked at by a stranger. It also saves a significant amount of battery when you switch the Bluetooth function off your phone when out of use.