BEIJING, Oct. 22 -- People using pirated Microsoft software in China are in the company's black books - with a screen to match.

The use of unauthorized Windows or Office applications now causes screens to turn black each hour, Microsoft's latest campaign to crack down on piracy in China which took effect yesterday.

The move has caused hot debate as Netizens labeled it a "monopoly act" and complained of the high price of genuine Microsoft products.

Some lawyers said the Microsoft initiative may cross a fine legal line.

Computers with Windows and Office applications, which fail an online validation check, will have screens turn black every 60 minutes, with pop-up alerts appearing that warn of piracy.

"Microsoft's Windows and Office Genuine Advantage will help users detect copycat operating systems," Microsoft said in a Chinese-language e-mail statement. "The move is just to warn users and not influence their normal operations."

All computers would return to normal after 45 days of black-screen warnings, Microsoft said.

On China's mainland, more than 90 percent of computers are installed with Windows and Office products.

About 40 million PCs are sold on China's mainland annually, which means Microsoft's move will influence millions of people.

The country's major government Website, www.people.com.cn, has initiated a poll regarding Microsoft's anti-piracy action.

Netizens were asked which ways they would prefer Microsoft to curb piracy other than the black-screen initiative.

More than 11,600 people had voted online by yesterday afternoon. About 79 percent said Microsoft should simply lower its product prices and about 12 percent questioned the legality of the action.