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Slack valuation more than doubles to $2.8 billion

Slack co-founder and CEO Stewart Butterfield
David Paul Morris | Bloomberg | Getty Images
Slack co-founder and CEO Stewart Butterfield

Six months ago, a year-old messaging app called Slack lit up the tech blogs when it raised money at a $1.12 billion valuation. Well, try $2.8 billion. (Tweet This)

That's how high investors including DST Global and Index Ventures are valuing the start-up, based on a $160 million financing round announced Thursday. All for a service that's effectively trying to kill internal e-mail use by simplifying communication among teams.

Created by Flickr co-founder Stewart Butterfield, the San Francisco-based company has over 200,000 paid users, and 750,000 people access the service daily. Customers include Adobe, the New York Times, HBO and Expedia.

Read MoreSlack: The billion-dollar accident

"Stewart and the team at Slack have taken a page out of the consumer playbook and revolutionized business communications by taking a generationally-different approach to messaging," said Mike Volpi, partner at Index Ventures and now a Slack board member, in the statement.

Slack didn't specify how it's going to put all this fresh cash to work, just months after raising $120 million. The biggest challenge is creating staying power in a market where many companies have emerged then fizzled. And there's competition from Atlassian's HipChat service as well as Asana and Basecamp.

"We're still at the beginning of a major transition in how people communicate and work together," said Butterfield.

The investing round was joined by all existing backers, including Andreessen Horowitz, Kleiner Perkins Caufield & Byers and Google Ventures.

Correction: An earlier version of this story misstated the company's October valuation.