Software developers like to use virtual machines because they can cheaply mimic a target environment.

Testers like virtual machines because they can test more combinations of new software with parts of the infrastructure in virtual machines.

Department heads like virtual appliances -- applications teamed up with an operating system in virtual machine-ready file format -- because they can be downloaded off the Internet, tried out, and pressed into service immediately, without the usual delays.

And each of these examples illustrates how virtualizing the enterprise leads to uncontrolled, virtual machine sprawl, with IT managers not knowing how many virtual machines they're running, where they're running, whether they're offline and stored away, or whether they're secure.

"I've had asset managers in some organizations tell me horror stories about how they're asked to license a virtual appliance in the next 24 hours because the trial period is about to expire, and the software is already in production," said Anil Desai, an independent consultant and author of the white paper "Controlling VM Sprawl."

"Those virtual appliances were never intended to go into production," because they haven't been configured by the IT managers for a given enterprise production environment. Nevertheless, he said in an inteview, "it happens all the time" that virtual machines and virtual appliances get deployed without the knowledge of IT staffs.

Desai also is the former solutions architect at Surgient, the virtual lab software supplier and hosting service in Austin, Texas. Desai added 350 servers during his 2004-2005 stint at Surgient as it became a host where Adobe Systems, BEA Systems, Microsoft, Siebel, and other firms demonstrated their software in virtual environments. As the hosting service grew, Desai ended up managing 3,500 virtual machines, averaging eight per server.

After leaving Surgient, Desai became an author and consultant focused on virtualization, Web services, and Windows Server technologies. At Surgient, he managed both VMware ESX Server and Windows Virtual Server virtual machines. He is the author of the books, "The Rational Guide To Managing Virtual Server" and "The Rational Guide To Scripting Virtual Server" (Rational Press, 2006).

As a frequent blogger and writer on virtualization, he was contacted by Embotics, a virtual machine management software firm, to write the Controlling VM Sprawl paper that was published Dec.18.