BOSTON, USA:Oracle Corp plans to acquire privately held virtualization software maker Virtual Iron, a move analysts said will put pressure on VMware Inc, the biggest player in the rapidly growing sector.

Oracle, the world's No. 3 software maker, announced the move on Wednesday, though it did not disclose terms of the transaction or say when it would close.

The deal also threatens to take business away from Citrix Systems Inc and Microsoft Corp, the other two key makers of virtualization software, help companies save money on hardware, energy and maintenance by enabling one piece of equipment to perform the work of multiple machines.

Market researcher Gartner estimates that sales of virtualization software will grow 43 by percent this year to $2.8 billion.

Analysts said Virtual Iron's technology is comparable to that of rivals, but the company has remained small because it has lacked marketing muscle and financing to take them on.

"Virtual Iron has a solid product," said Jefferies & Co analyst Katherine Egbert.

Oracle, the world's biggest maker of database software, has one of the software industry's largest sales forces and will likely use its marketing infrastructure to sell Virtual Iron products alongside other business software.

The company can package the products together, offering discounts and tweaking the virtualization programs so that they better work with Oracle's database software, middleware and business management programs.

"If I were VMware, if I were Microsoft, if I were Citrix, I would be concerned," said ITIC analyst Laura DiDio. "Oracle's mentality when it comes to rivals is very simple: 'Take no prisoners.' They are a very, very tough competitor."

Lowell, Massachusetts-based Virtual Iron's technology will augment virtualization programs that Oracle introduced in late 2007. That software, dubbed Oracle VM, is primarily used with computers running on the Linux operating system. It competes with virtualization software from Red Hat Inc and Novell Inc .

Virtual Iron's programs are primarily used in the far larger segment of the virtualization software market -- machines running on Microsoft's Windows server software, which is where VMware dominates, followed by Microsoft and Citrix.

Redwood City, California-based Oracle is also poised to gain other virtualization products with its planned purchase of Sun Microsystems Inc  for more than $7 billion, which it announced last month.

Oracle shares were down 1.7 percent at $18.06 on the Nasdaq on Wednesday afternoon. Shares of VMware were down 4.1 percent at $26.68. Microsoft shares were down 0.6 percent at $19.77 and Citrix was down 3.4 percent at $26.82.