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This will have future implications of existing exchanges should this happen.
I can see Govt's getting involved to "regulate" say Poloniex to try to stop this from happening.
Problem is that there are other services that exist to facilitate this method of washing coins, and if those ever got shut down there would be some other avenue to do so.
It's a matter of time before the usage of monero in that manner is taken advantage of.
Right now monero is not really on the radar, at least not yet.
Edit: If polo or an exchange tracking the hacked coins decided to block those coins from being deposited and converted to say XMR, those implications would be interesting to see unfold. I would expect a hacker to deposit in different places utilizing shapeshift.io and xmr.to.
I reckon that it would be difficult to block all avenues to "wash" coins from a hack in this manner. But then again it is something to watch for in the future given the technology that XMR has let out of the genie bottle.
but this all remains to be seen.
The already do. The issue with money laundering on such a large scale is not whether the governments can prevent it, they can. It is can they effectively punish a bank that engages in money laundering without destabilizing the whole debt based fiat banking system?
The US government decided not to pursue criminal charges against HSBC for allowing terrorists and drug dealers to launder millions of dollars after George Osborne and the UK banking regulator intervened to warn that prosecuting Britains biggest bank could lead to a global financial disaster.
https://www.theguardian.com/business/2016/jul/11/hsbc-us-money-laundering-george-osborne-report With crypto currency such a Monero this could work since punishing a rouge player would not destabilize the rest of the financial system since it would not be debt based.
Edit: MTGox did not kill Bitcoin neither will BitFinex.