Big banks certainly appear safe, as they have eased up on trading subprime mortgage-backed securities, which were in part the result of the last financial crisis, but with continued trading of derivatives on everything from corn prices to credit-default swaps, banks are still vulnerable.

The trading of derivatives, which Warren Buffett once called "weapons of mass destruction," is still a hot topic in terms of regulating the primary cause of the financial crisis in lieu of the lenient new regulations that have been applied to big banks, The Huffington Post reported.

According to a recent report from a group of the world's financial watchdogs, including the Federal Reserve, banks can't always determine who is on the other side of their trades, which is risky.

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"Five years after the financial crisis, firms' progress toward consistent, timely and accurate reporting of top counterparty exposures fails to meet supervisory expectations as well as industry self-identified best practices," the regulators wrote.

In other words, banks still don't know the outcome of trading derivatives should they go horribly wrong, according to The Post.

The Lehman Brothers scandal that started the financial crisis is a prime example of how banks don't do a good job of understanding their exposure to huge losses on derivatives.

What was the worst financial crisis since the Great Depression could happen again should banks choose to stay in the dark, The Post noted.

"On derivatives, the global financial system was flying blind," said Francesco Guerrera, financial editor of The Wall Street Journal. "It still is, albeit less so, according to the 10 regulators."

New regulations have not been effective, as banks are not keeping track of their derivative trades because of the painstaking burden and costs associated with the required paperwork, according to Guerrera.

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