Citrix Systems has bought QuickTree, a software developer focused on improving security and performance for XML and Web services.

QuickTree software can be added to network gear to guard against attacks carried within XML traffic. The company’s XML Security Module (XSM) processes and inspects XML traffic as it passes through these devices, such as firewalls, load balancers and SSL VPN gateways.

Citrix says it plans to add these capabilities to its NetScaler application-acceleration platform, WANScaler WAN-optimization gear and to its Citrix Access Gateway SSL VPN device.

Competitors include Layer 7, Cisco with its purchase of Reactivity and Forum Systems.

Citrix argues that while stand-alone XML appliances are one way to boost XML processing speeds and secure XML traffic, it is more efficient to integrate these features in existing network infrastructure. Such equipment would reduce the number of devices in the network and ultimately scale better than appliances, Citrix says.

Citrix says it will integrate XSM into its AppExpert Policy Builder platform, a GUI tool for creating policies for applications and users that are translated into rules that are enforced by Citrix network infrastructure.

The company says XSM will be integrated first with NetScaler, which typically sits between Web servers and the larger private or public IP network.

Citrix did not disclose how much it paid for QuickTree. All QuickTree employees will join Citrix as part of its Application Networking Group.

This purchase comes just two weeks after Citrix bought XenSource, which brings server virtualization technology to the company. Citrix says that will also include shared storage, resource sharing and management.

Earlier this summer Citrix bought the assets - mainly developers - of defunct SSL VPN and NAC vendor Caymas Systems. They have also been assigned to Citrix’s Application Networking Group.

Citrix has expanded its product range greatly over the past two years with significant investments in new technologies:

* XenSource, $500 million, closed August 2007. This gives Citrix virtualization technology.

* Caymas Systems assets, undisclosed price, brings SSL VPN and NAC expertise.

* Orbital Data, $50 million, announced in August 2006. The acquisition gave Citrix the ability to tinker with how data is sent over WAN connections so it is transferred more efficiently, giving users the feel that the link is faster.