Earlier this week Apple CEO Tim Cook wrote an open letter to the American public about the FBI's attempts to compel the company to crack the iPhone of the San Bernadino Jihad attackers, saying that such a tool for the government is too dangerous to create. Google, Facebook and Twitter have now joined Apple in the phone encryption battle.

As explained by The Intercept, here's a brief overview of what the FBI wants Apple to do:

The most obvious way to try and crack into your iPhone, and what the FBI is trying to do in the San Bernardino case, is to simply run through every possible passcode until the correct one is discovered and the phone is unlocked. This is known as a "brute force" attack.

One obstacle to testing all possible passcodes is that the iPhone intentionally slows down after you guess wrong a few times. An attacker can try four incorrect passcodes before she's forced to wait one minute. If she continues to guess wrong, the time delay increases to five minutes, 15 minutes, and finally one hour. There's even a setting to erase all data on the iPhone after 10 wrong guesses.