Slack, the interoffice chat program that has reframed how many companies talk to themselves, has been growing at a meteoric rate based mostly on word of mouth. Now their chief executive wants to get serious about growth — and that means IT needs to be paying attention.

It’s something I’ve been thinking about for a few months, as business after business I’ve talked to has had users bring Slack in, generally without asking IT’s permission, and conducting work (and personal) discussions on it.

How quickly it was being adopted by major players and how dangerous that could be was put on display a year ago when a security flaw — originally meant as a feature — showed the various Slack groups of a company to anyone clever enough to put in a fake corporate email address. Then last spring attackers gained access to Slack’s database of usernames, email addresses, and other profile information.

That hasn’t slowed Stripe’s growth. Earlier this month, at Web Summit, Stewart Butterfield said that now that his company has a sizable warchest, they were going to start ramping up marketing efforts (emphasis mine):

“We are switching from trying to keep up with growth to trying to generate growth,” Butterfield said in an interview at Web Summit, Europe’s biggest conference for start-ups.

“Slack can afford to pay a pretty high price to acquire paid users. If we are able to grow this company through advertising, that is my preference,” he said.

The move comes even though Slack is already growing at more than 10 percent per month and has acquired 480,000 paid users since it was introduced 21 months ago, Butterfield said. Including free customers, it counts 1.7 million daily active users.

Slack’s team messaging software has gone viral over the past year among business users while often flying under the radar of information technology departments.)

Almost two million users discussing corporate crown jewels, growing at 10 percent a month, with two major security breaches — and IT is largely out of the picture. The good news is that Slack has been working hard to be friendly with IT, with features like compliance exports, user provisioning, and much more available now and down the road. The bad news is that, for many companies, if IT doesn’t embrace Slack, end users likely will, creating a shadow intranet that is out of sight, out of mind, and a big blind spot just waiting to cause problems.