Slack shares whipsaw amid confusion over IBM contract

Slack shares soared and trading in the workplace collaboration company was briefly halted on Monday, after a report stating the company had landed IBM as its biggest-ever customer.

Yes, but: The thing is, IBM was already Slack's largest customer and has been for a couple of years. In an SEC filing, Slack said IBM has been adding additional Slack licenses over time and that it is not changing its financial forecast for the current quarter.

IBM's use of Slack began in 2014, with a group of 68 engineers and grew from there. IBM was one of the first users of Slack's Enterprise Grid and had more than 165,000 users by last year. Today it has more than 300,000 users and offers slack to all employees.

Why it matters: Microsoft has been increasingly going after Slack with its Teams product, which it bundles with Office. Slack has been eager to show its chops, especially among larger businesses that Teams isn't yet equipped to handle.

By the numbers: Shares of Slack ended regular trading on Monday at $26.54, up $3.55, or more than 15%. However, the stock fell in after-hours trading after Slack made its SEC filing, changing hands recently at $24.85, down $1.69, or more than 6%.