There has been a lot of bad news on cryptocurrencies lately involving exchange fraud, hacks, and government investigations. Bitcoin dropped from $11,650 to $8,800, a 25% mini-crash, in just a few days between March 5 and March 8 based on this barrage of bad news.

Still, all of this drama may be small potatoes compared to the one time bomb that could blow up the $400 billion market capitalization of the entire cryptocurrency market. That time bomb is called “tether.”

Tether is not intended to go up or down in value like other cryptos. One tether (USDT) is intended to always equal one dollar (USD). When you buy USDT in exchange for USD from the Bitfinex crypto-exchange, Bitfinex says they put the dollars in a kind of escrow so they’re available when you want to cash out for dollars. In turn, the tethers are widely used in crypto-exchanges as a kind of stable value substitute.

It’s much easier to move USDT around crypto world then to move in and out of the USD. (And don’t even ask about the tax consequences of this; that will really make your head hurt).

As this article describes, many in crypto world are questioning the assumptions behind tether. Are the dollars really there to back them up? What if Bitfinex just issues tether to prop up their bitcoin trading without keeping the dollars in escrow? That would be tantamount to counterfeiting dollars to prop up bitcoin.

There has been a lot of bad news about tether and Bitfinix lately. An auditor hired to provide proof of the Bitfinex claims was dumped. As of now, there is no audit.

U.S. government agencies have subpoenaed Bitfinex and tether so presumably they’ll get to the bottom of this. Perhaps all is well. But, if tether turns out not to have the dollars behind them that they claim, it’s just a matter of time before there’s a “run on the bank” in cryptocurrencies. Tether will not be the only victim.

Since tether is so widely used, we’ll see the entire interconnected network of crypto-currencies and crypto-exchanges come crashing down. The $400 billion market capitalization of the entire crypto-world will be mostly wiped out.