Why Did China's ATMs Stop Working Last Sunday?

A lesson for all around the globe, keep some cash outside the system.

Bloomberg reports:

[Last] Sunday morning, while China was taking a weekend breather from the financial fireworks caused by the government’s weeklong self-inflicted cash and credit crunch, customers of the Industrial and Commercial Bank of China, the world’s largest bank, woke to an unpleasant surprise: Their deposits were not available for withdrawal by ATM or teller (online or in-person). 

The social-media reaction was swift, filled with exclamation points and lacking in confidence for ICBC, or the Chinese banking system as a whole. “I was just at ICBC to make a withdrawal and was told the system was undergoing an upgrade and withdrawals are temporarily unavailable,” tweeted a user in Shenyang on Sina Weibo, China’s leading social-media platform. “I called the service hot line, finally someone answered and said they don’t know the answer!!!!!!! ICBC: When can we withdraw money? Who can give a clear answer??????????????”