First it was Dropbox.

Two weeks ago we reported that one of the numerous "unicorns" prancing around Silicon Valley was about to have a very rude wake up call when Dropbox was warned by its investment bankers that it would be unable to go public at a valuation anywhere near close to what its last private round (which had most recently risen to $10 billion from $4 billion a year ago) valued it at.

Than it was Jack Dorsey's "other" company, Square.

Last last week: "today another company realized today just how big the second "private" tech bubble, one we profiled first in January of 2014, truly is. That company is Jack Dorsey's Square, which earlier today filed a prospectus in which it said that the "initial public offering price per share of Class A common stock will be between $11.00 and $13.00." Assuming a mid-point price of $12 and applying the 322.9 million shares outstanding after the offering, it means a valuation of $3.9 billion. The problem is that in its last private fundraising round, Square was valued at about $6 billion according to ReCode."

Today, it's the turn of Snapchat, the fourth most highly valued private tech start up.

According to FT, "Snapchat has been marked down by one of its most high-profile investors, raising further questions about the soaring valuations of private technology companies. Fidelity, the only fund manager to have invested in the four-year-old company best known for disappearing photos, wrote down the value of its stake by 25 per cent in the third quarter, according to data from investment research firm Morningstar. It had valued each share at $30.72 at the end of June but dropped the valuation to $22.91 by the end of September."

It is unclear why Fidelity marked down its stake but Snapchat is still searching for a sustainable revenue model.

It is also unclear if other Snapchat investors, such as VC titans Benchmark and Kleiner Perkins, as well as tech companies Alibaba, Tencent and Yahoo have followed Fidelity into what is becoming a widespread realization that not only was there a private tech bubble, but that it has burst.

A bigger question is whether it will be a controlled demolition as unicorns everywhere are demoted to what we first dubbed "zerocorn" status in the coming days. To be sure, the VCs are desperate for a controlled demolition, and hoping the broader market ignores the euphoria that took place in Silicon Valley over the past 3 years, is now over, and that giddy investors overshot by at least 25-35% to the upside in the past several private funding rounds as everyone was rushing to pass the valuation hot potate to ever greater, and richer, fools.

It remains to be seen how successful they will be, and just what the source of capital for hundreds of "$1+ billion"-valued, cash burning companies will be in lieu of generous VCs, and just how viable the second tech bubble will be if these hundreds of companies suddenly are forced to generate cash flow to fund themselves.

One thing we know: there sure are many of them, as this infographic from the WSJ proves:

And here is the stunner: the combined "valuation" of total US unicorns is $486 billion. Their combined profit? $0.