Wayne, Pa.-based Kenexa utilizes cloud-based technology and online social media tools to assist clients in staff development and consulting tasks. The target has some 8,900 customers in several industries, including financial services, pharmaceuticals, retail and consumer. It has about 2,800 employees.

Kenexa will complement IBM's social media business and human resource business services offerings, IBM said.

"The combination of our two organizations will deliver more business outcomes than ever before," Kenexa CEO Rudy Karsan said in a statement.

"Together, Kenexa and IBM will be unmatched in the industry, offering solutions that extend from strategy to the technology platform to the delivery of services for clients," Karsan added.

Armonk, N.Y.-based IBM is looking to tap into the increased pervasiveness of social media in the business world and broader economy.

A November 2011 report from Forrester Research Inc. stated the market opportunity for social enterprise applications is expected to increase at a rate of 61% through 2016.

"The acquisition of Kenexa aligns to IBM's business analytics growth road map, which IBM projects to be $16 billion in revenue by 2015," IBM spokeswoman Karen Lilla said.

IBM expects the transaction to close in the fourth quarter, subject to Kenexa shareholder and regulatory approvals and other customary closing conditions.

On Aug. 16, IBM announced an agreement to buy flash memory producer Texas Memory Systems Inc. of Houston for undisclosed terms. The deal was a rare add-on for IBM in the hardware and data-storage-techology market; it typically focuses its M&A more on software.

Kenexa didn't return calls.

Kenexa shares shot up $13.44, or 41.49%, to $45.83, in early trading Monday. IBM shares were down 62 cents, or 0.31%, to $197.15.

Cravath, Swaine & Moore LLP's Scott Barshay was counsel to IBM. Kenexa turned to Lazard's Alex Stern and Paul Haigney and Pepper Hamilton LLP's Barry Abelson.