Have there been case of crypto hack? If so, how do the hacker get those huge amount of crypto into traditional banks without attention from government?

Yes, there have been several cases of crypto hacks. Some of the most notable ones include the Mt. Gox hack in 2014, the Coincheck hack in 2018, and the Binance hack in 2019.

In terms of how hackers get the stolen crypto into traditional banks without attention from the government, there are several ways they can do this. One common method is to use money laundering techniques such as "mixing" or "tumbling" the stolen crypto through multiple addresses and exchanges to obfuscate its origin before converting it into fiat currency and depositing it into a bank account. Another method is to use offshore bank accounts or shell companies to hide the source of the funds. However, it's important to note that these methods are illegal and can result in severe consequences if caught.