"The so-called consumerization of IT is a trend which I think perhaps more than almost any other company out there Yammer has gotten right," Ballmer said.

ESN software provides Facebook- and Twitter-like capabilities adapted for workplace use, including employee profiles, activity streams, discussion forums, microblogging, wikis, idea generation software, joint document sharing and editing as well as tagging, rating and reviewing of content.

ESN products have become popular in recent years as tools that, when properly implemented and adopted, can improve the way employees collaborate and communicate, leading to increased efficiency and productivity, by complementing traditional applications like email and instant messaging.

Spending on ESN products grew almost 40 percent last year to $767.4 million, and is expected to grow at a 42 percent compound rate through 2016, when it will reach almost $4.5 billion, according to IDC.

Yammer competitors include Jive Software, NewsGator, Socialtext and Tibbr. In addition to ESN specialists like Yammer, larger software vendors have also been adding ESN features to their broader collaboration suites and enterprise applications, including IBM, Oracle, Salesforce.com and Cisco.