Microsoft said on Tuesday it had started 55 legal actions around the world against dealers it accuses of selling counterfeit software online, its largest enforcement effort to date.

"Today's announcement marks ... the first time the company has focused its efforts worldwide to bring legal action against online dealers," the U.S.-based software company said in a statement.

The legal actions include 15 in the United States, 10 in Germany, 10 in the Netherlands, five in France and five in Britain, as well as proceedings in Argentina, Australia, Belgium, Korea, Mexico and Poland.

The cases are against sellers who the company says have misused their eBay or other online auction site accounts to sell counterfeit software. Microsoft said it had sent warnings for infringing behavior to many of the defendants before taking the legal action.

Microsoft analyzed counterfeit Windows XP programs in June this year and said it found that 34 percent of the disks could not be installed on a computer, and another 43 percent contained additional programs, or binary code, that are not part of the operating system.