The European Union reported on Tuesday that some 100 million Europeans using Microsoft Corp. software will be asked to choose among rival Web browsers by mid-May. This comes under a deal which the EU struck with the firm in order to settle the latest antitrust action.

Microsoft, this month, is starting to send updates to Windows computers in Europe so that when computer users log on, they will see a pop-up screen asking them to pick one or more of 12 free Web browsers to download and install, including of course, Microsoft.

The European Union’s executive commission said that giving consumers the chance to try an alternative to Microsoft’s Internet Explorer browser, which comes with the widely used Windows operating system would

“bring more competition and innovation in this important area.”

EU antitrust regulators in December dropped their last pending antitrust case against the software giant, after the company offered to let users choose between its browser and others. This ended more than a decade of legal trouble which cost Microsoft, euro1.7 billion in fines.

Rivals had complained that attaching Internet Explorer to Windows was an excessive way for Microsoft to put its Web software on most of the world’s computers.

The top five browsers: Microsoft’s Internet Explorer, Mozilla’s Firefox, Google Inc.’s Chrome, Apple Inc.’s Safari and Opera, will be given prominent placement on the pop-up choice screen.

The selections will rotate from computer to computer, so none of these five browsers will always be first.

Smaller competitors such as Avant Browser, Flock, Green Browser, K-Meleon, Maxthon, Sleipnir and Slim Browser will also be displayed when the user scrolls sideways.

The EU said greater browser choice also would boost the use of open Web standards: a set of guidelines on how Web sites are designed.
Rivals claim that Microsoft has not always followed these standards closely, thereby forcing Web designers to make sites compatible with Internet Explorer — the leading browser — instead of working smoothly with other Web software.

Microsoft’s browser choice screen will be used for five years in the 27-nation European Union plus Norway, Iceland and Liechtenstein.

Microsoft could be fined 10% of its annual revenue if it does not stick to its commitment to distribute the browser screen and avoid any retaliation against computer manufacturers who install other browsers as a default on the computers they sell.

Users in the U.S. and elsewhere will not see any change.