Have you heard of the term IMSI Catcher?
Your phone may be being tapped right this second, by the government, police, or even criminals in your area; and it's not hard either. That's not just phone calls, but texts, and data too. It doesn't matter whether you have an iPhone, Blackberry, or Android device, you're being intercepted and there's almost nothing you can do about it.
But wait... what is an IMSI Catcher?
International Mobile Subscriber Identity, or IMSI, is a system used for authenticating your phone with your network. Due to flaws in 2G, 3G, and recently even 4G (LTE), this system can by attacked, allowing people to intercept your communications.
IMSI Catchers are devices that are readily available on the black market (including various online markets similar to Silk Road), as well as sold in the open to law enforcement by various companies. They allow someone to run a fake cell tower allowing them to intercept calls, data, and texts to and from your phone, sometimes regardless of the network.
Don't believe me? Here's several companies offering them on the open internet (to law enforcement/government):
- http://www.rayzoneg.com/en.piranha.html
- http://www.discoverytelecom.eu/catalog/2196.html
- http://www.pki-electronic.com/products/interception-and-monitoring-systems/3g-umts-imsi-catcher/
I'm a not a criminal! Why would they target me?
They don't need to think you are. Did you know they can be used by the police in most countries without a warrant?
IMSI-catchers are often deployed by court order without a search warrant, the lower judicial standard of a pen register and trap-and-trace order being preferred by law enforcement
https://en.wikipedia.org/wiki/IMSI-catcher
To top it off, as mentioned earlier, these can be obtained by actual criminals, who could use them to intercept your calls, texts, and data. Potentially hacking your accounts, bypassing 2-Factor authentication via texts, or even blackmailing you based on your calls.
Is there any way to stop this?
You can reduce the risk by limiting your phone to 4G networks. Those are harder to attack, but still not perfect.
You can detect if you're being attacked on Android by installing IMSI Catcher Detector available here: https://github.com/CellularPrivacy/Android-IMSI-Catcher-Detector - it doesn't require root, and is open source. Note that it can only detect the attacks, it can't fully stop them from happening, but you'll at least know if you're being monitored.
For users of other phones, your only bet is to watch your carrier information in settings. Some poorly made IMSI Catchers can cause your Carrier Name to change to some odd, such as random numbers or characters.
Conclusion/TLDR
If you're in a major city such as San Francisco, London, Berlin, etc. you're probably surrounded by IMSI Catchers. London is a major hotspot for them. If you have an Android phone, you can install IMSI Catcher Detector to help protect yourself. For all others you're out of luck.
It's depressing to know that even the latest network technology, 4G, is vulnerable to these attacks still. We can thank the government for that, as they're often involved in the decisions allowing them to intercept our communications.