Remember that vulnerability in the SS7 inter-carrier network that lets hackers and spies track your cellphone virtually anywhere in the world? It's worse than you might have thought. Researchers speaking to Australia's 60 Minutes have demonstrated that it's possible for anyone to intercept phone calls and text messages through that same network. So long as the attackers have access to an SS7 portal, they can forward your conversations to an online recording device and reroute the call to its intended destination. This helps anyone bent on surveillance, of course, but it also means that a well-equipped criminal could grab your verification messages (such as the kind used in two-factor authentication) and use them before you've even seen them.
I wrote about cell phone tracking based on SS7 in Data & Goliath (pp. 2-3):
The US company Verint sells cell phone tracking systems to both corporations and governments worldwide. The company's website says that it's "a global leader in Actionable Intelligence solutions for customer engagement optimization, security intelligence, and fraud, risk and compliance," with clients in "more than 10,000 organizations in over 180 countries." The UK company Cobham sells a system that allows someone to send a "blind" call to a phone--one that doesn't ring, and isn't detectable. The blind call forces the phone to transmit on a certain frequency, allowing the sender to track that phone to within one meter. The company boasts government customers in Algeria, Brunei, Ghana, Pakistan, Saudi Arabia, Singapore, and the United States. Defentek, a company mysteriously registered in Panama, sells a system that can "locate and track any phone number in the world...undetected and unknown by the network, carrier, or the target." It's not an idle boast; telecommunications researcher Tobias Engel demonstrated the same thing at a hacker conference in 2008. Criminals do the same today.