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Four million current and former federal employees are dealing with uncertainty today after their information was compromised in a breach of the Office of Personnel Management.

Reports indicate that the attack originated in China, though officials there have denied any wrongdoing.

"We know that hacker attacks are conducted anonymously, across nations, and that it is hard to track the source. It's irresponsible and unscientific to make conjectural, trumped-up allegations without deep investigation," Chinese Foreign Ministry spokesman Hong Lei said Friday.

This is not the first time the United States and China have blamed each other for such activities. Earlier this year, Mike McConnell, former director of the NSA, said that China had hacked every major U.S. corporation, as well as Congress, the Department of Defense, and the State Department. And in the wake of the Snowden revelations of NSA spying, Huang Chengqing, director of the National Computer Network Emergency Response Technical Team/Coordination Center of China, said "we have mountains of data, if we wanted to accuse the U.S."

While both countries will likely never be able to verify exactly who is hacking whom, check out the slideshow for some other times the U.S. and China have been at odds over hacking accusations.