5. Palo Alto Networks

Despite a slight drop in the number of units sold year over year, Palo Alto Networks landed at the No. 5 spot for most network security units sold. The Santa Clara, Calif.-based company sold 6,150 units in Q1, down 9.4 percent year over year. The company held a 6 percent unit market share for the quarter, down from 5 percent in Q1 of last year. While the company has been launching new security appliances, including six last quarter, it has been investing big in expanding and updating its subscription services, including a major PAN-OS update in February and its February acquisition of behavioral attack detection company LightCyber.