If you had a skill to hack $2.3B you'd definitely found the way how to launder it. So many ways to do it: deep net, mixers, scam exchanges, OTC private deals, multiple wallets etc. I think they will be ok if don't make some stupid mistake which is possible too.
How on Earth does one even begin to launder $2.3 billion. They will have to have like 100 corrupt politicians in their back pocket. Really, you need government cooperation to launder that kind of money. And they probably can never travel outside the country where they cash out.
I have to disagree with you. Laundering this many coins is actually harder than stealing them. Hacking an exchange can be done in a few steps, if the insiders are involved. However, moving this money and then converting them to fiat can be quite complicated. Staying anonymous during this step is next to impossible. The least risky strategy is to move the coins from one crypto wallet to another a few times and then mixing them. The conversion to fiat should be done after many years, after making sure that the trail can't be traced back. In many cases, the hackers don't have the patience for all this and ends up revealing their true identity.
Will they be able to liquidate those BTC on decentralized exchanges or convert that amount for another cryptocurrency?
