IBM shares were up around 4% to $120.22 on news of the buy.
Late last month, IBM announced plans to buy back $4 billion in shares over time in a stock repurchase program.
The purchases come after IBM announced plans late last month to buy the open source cloud software provider Red Hat (RHT) - Get Report at $190 per share in cash. The purchase was IBM's largest, reported Bloomberg.
Calling the Red Hat deal a "game-changer," Rometty said the purchase would make the company the world's No. 1 "hybrid cloud provider."
With a two-decade partnership with Red Hat, IBM has long worked with the Linux-based company on cloud products for its $19 billion hybrid cloud business.
Earlier in October, IBM reported its third quarter earnings, which showed revenue down 2% at $18.8 billion.