So you’ve made a ton of money from bitcoin, Ether and other cryptocurrencies. Sure, they’ve defied the doomsayers time and again. Which likely makes this week’s shocking plunge in bitcoin and Ether just another buying opportunity. That’s where you may be wrong.

The sudden Chinese crackdown on the virtual coin fundraising of bitcoin BTCUSD, -1.58% and other cryptocurrencies that caused the plunge is either the end of the beginning for the crypto-party — or, more likely, the beginning of the end. If you’re holding cryptocurrencies today, remember that no matter how much money you think you’ve made, you haven’t made a nickel until you’ve cashed it out.

And you might want to think twice, or even thrice, about the rising risks.

China took steps on Monday to stop “initial coin offerings” or ICOs. These are the crypto-bubble equivalent of the infamous IPOs during the late 1990s dot-com mania.

Additionally, Hong Kong’s regulator warned that cryptocurrencies may be securities for legal purposes and that these ICOs may be subject to securities laws — echoing similar rumblings from the U.S. Securities and Exchange Commission.

Read: Confused about bitcoin? 10 things you need to know

This isn’t just a passing cloud. This is potentially a big deal. Blockchain technology may be as amazing as its proponents claim. But translating that into a financial mania for cryptocurrencies depends on some huge, and flawed assumptions. First among them: the idea that governments are just going to sit idly by and let cryptocurrencies flourish.

Sure, cryptocurrencies could be used by all sorts of lovely people for all sorts of lovely things. But shadow, unregulated currencies can also be used by say, tax evaders, drug dealers, money launderers and other criminals.

Oh, yeah, and terrorists. Who’d a thought it?

You see, after 9/11 there was a massive international crackdown of financial regulation around the world, including intense pressure on jurisdictions which had previously turned a blind eye to shadow finance and money laundering.

It is possible, but extremely unlikely, that financial regulators worldwide are going to wait for another 9/11 to do this again.

When these cryptocurrencies were small, it didn’t matter. But last week their total market value hit $150 billion and this number has been heading up. Do you think governments are going to be okay with a $150 billion financial network that can be used by anyone outside of any oversight? How about $300 billion? Or $3 trillion?

Read more: One huge chart showing bitcoin’s incredible rise to $4,800

It makes no serious sense. In other words, cryptocurrencies lack precisely the supposed unlimited upside that speculators dream about. The only way we are ever looking at so-called “blue sky” valuations is if the governments of the world all lose their collective minds.

This technology may forever change how you sleep

And as for those cryptocurrency fans and their libertarian fantasies: If you think bitcoin or Ether or whatever is somehow beyond government control because it is so decentralized across so many different computers, think again. Governments may not be able to shut down all the servers, but they don’t have to. They can in theory ban people and companies under their jurisdiction from buying, selling, trading, or holding these things. Governments can make your cryptocurrencies unconvertible into anything useful.

Don’t forget, the U.S. government successfully bigfooted online poker companies a decade ago, even though those operated from outside any U.S. jurisdiction. Cryptocurrencies are no safer.

Those speculating on cyber currencies have now received warnings from the financial regulators of the world's two biggest economies. This looks very much like something coordinated. Regulators do not want to ban something without any warning. If they did, they'd risk hurting many mom and pop investors who are naively taking part. A series of escalating warnings, as we are seeing now, leaves the innocent fewer excuses.

There were signs on Tuesday that crypto fans are betting that this, too, will pass. Currencies and tokens bounced sharply after the selloff. And while bitcoin now is well-below its peak of almost $5,000 hit last weekend, it’s still up a storming 35% over the past month.

Crypto-mania may continue for now. Traders will be watching the charts to see how the trends develop. But the long-term investment story looks like another matter. The risks are rising.