Network Security Company Tenable Raises A $50M Series A From Accel

Tenable Network Security, which was founded back in 2002, has raised its very first round of institutional funding — specifically, a $50 million Series A from Accel Partners.

Accel makes it share of normal venture investments, but it also likes to find mature, bootstrapped companies and offer them big checks. (Other deals in this vein include the $60 invested in Atlassian and the $70 million invested in Qualtrics.) In this case, Accel partner Ping Li says he has been “stalking these guys, for lack of a better word,” for several years, in part because Tenable products, especially Nessus, are being used by a number of Accel’s portfolio companies.

In fact, Tenable says that its customer base now includes 15,000 organizations — including the US Department of Defense, Barclays, Visa, Amazon, Apple, Google, AT&T, Verizon, and many others — creating a user community with more than 1 million people. The company also says that its revenue has grown more than 550 percent over the past four years.

And Li, who’s joining Tenable’s board of directors, says there’s still a big opportunity here, in part because Tenable is equipped to deal with emerging threats like mobile, social networking, virtualization and the cloud — threats that make network security important beyond large enterprises. The company is also growing internationally, with installations in 150 countries, and Tenable plans, in part, to use the new money to continue that expansions.

The company’s team says that one of its key advantages is the fact that it’s not just doing a traditional security audit every week or month, but also passively monitoring the network, all the time. In mobile, for example, Tenable can’t scan every device during an audit, because many of those devices are sleeping. But during the passive monitoring period, Tenable can still look at device traffic for “telltale signs” of vulnerabilities.

“Mobile and virtual have really changed the way that IT shops are having to exist,” says Tenable President and COO Jack Huffard. “We felt to in order to really make this a big, standalone company, we needed to get into those markets fast, and we needed a partner that can help us do that.”

Oh, and here’s a fun video visualizing an office network that Tenable shared earlier this year.