The deal was announced on XDN's blog Wednesday with a little bit of fanfare but no details.

Fortinet isn't exactly interested in building a CDN of its own. Rather, Fortinet saw a chance to beef up its software abilities in cloud management, says John Maddison, Fortinet's VP of technical marketing.

Fortinet sells security appliances, and lately it's been getting into cloud-based management of network security. XDN, with its expertise in areas such as domain name system (DNS)-based load balancing, could make a good fit with products such as FortiWeb (an application-security appliance) and FortiDNS (a caching DNS server), Maddison tells Light Reading.

Long-term, he sees a hybrid model for security emerging, one that combines customer-owned equipment with cloud-based layers of functionality. That's in contrast to the fully cloud-based security model envisioned by startups like Zscaler.

Originally named 3Crowd, XDN was founded by Barrett Lyon, founder of CDN provider BitGravity -- and naturally, XDN grew out of lessons from that experience. He found that BitGravity needed a partner that had bandwidth and storage handy, and that led to a partnership with -- and an eventual acquisition by -- Tata Communications Ltd.. (See Tata Comms to Buy BitGravity.)

"I realized at the end of it that we should be doing it with just one carrier. We should be doing it with all the carriers," Lyon, who left BitGravity in 2009, told Light Reading last year.

XDN decided to use its software to let operators build their own CDNs out of available network resources, doing so via a Java client that connected servers back to XDN's controller. It was an alternative to traditional CDN's, where the software "takes over an entire server," as Lyon described it, creating a distributed entity that resembled a botnet but was less, you know, evil.

OnApp launched a similar service last year around the same time XDN did. (See Hey, Guys, Let's Build a CDN!)

Fortinet isn't revealing any details about the XDN deal, but we can guess that it wasn't exactly huge. XDN raised a $6.6 million Series A round in 2010 and had just 20 employees as of April, according to GigaOm.

— Craig Matsumoto, Managing Editor, Light Reading