Andreessen Horowitz just doubled down on an investment in a security startup called Tanium.

The VC powerhouse already plowed $90 million into the company in May 2014, at a valuation of about $900 million, according to PitchBook Data, a company that tracks private equity funding through the documents filed.

On Tuesday, the firm announced another $52 million investment. 

PitchBook tells us with the new round, the startup is now worth $1.75 billion, making it among the most valuable enterprise startups around.

At the center of both investments is Steven Sinofsky, Microsoft's former Windows leader. He's now a board partner at Andreessen Horowitz, meaning he helps find investments and serves on the boards.

Tanium impressed him into $142 million in nine months with the pedigree of its founders, its technology, and its growth.

The startup was conceived in 2007 by father/son team David and Orion Hindawi, who had worked quietly on developing the tech for about five years, they say.

This was their second gig together. They worked for about 18 years at the previous company father David founded, BigFix, which sold to IBM in 2010 for a reported $400 million.  Orion was a product manager at BigFix.

Prior to meeting Sinofsky and landing that first $90 million, the two had raised $812,000 in seed money from undisclosed investors, according to CrunchBase.

Tanium solves a big problem that Sinofsky is very knowledgeable about: Knowing when PCs and other devices (servers, ATM machines) are having problems or are the target of a hack.

Tanium tells IT folks about such problems within 15 seconds, it says. That means IT folks can see problems or a hack attack as it is happening, almost in real time, including which devices are having problems and how many are affected. IT pros can then use Tanium to shut down the device or for "quarantining devices, alerting users, or patching the appropriate modules, all in seconds rather than days," Sinofsky describes in a blog post about the investment.

Instant security like that is the holy grail for IT folks. And the situation is only going to get more intense as more everyday objects get chips and sensors and join the Internet of Things and corporate networks.

The company claims it's growing like crazy. In 2014, it quadrupled growth in total billings and its headcount. It now employs 150 people, it says.

It also landed more big contracts and now counts five of the top 10 US banks, four of the top 10 US retailers, and fifty of the Fortune 100 as customers, the company says.

It's also bringing in plenty of cash, staying profitable and "debt free," it says. In 2014, the company landed several deals valued at over $1 million and even some deals at over $5 million, it says, and has total cash in excess of $100 million, it says.

Even with that stockpile of cash, it took Andreessen Horowitz's second investment. The company says it will use the extra cash to hire, beef up its products, and expand into Europe and Asia. Sinofsky, as you might expect, sits on its board.

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