The Associated Press

NEW YORK - Microsoft Corp. chairman Bill Gates is boasting that the software giant will spend $300 million to promote the latest version of its Internet service.

He may have underestimated by just a bit.

After plastering city sidewalks, streets and other public property with butterfly-shaped advertising decals, New York City has sent Microsoft a $50 summons.

Microsoft vice president Yusuf Mehdi said the company was sorry.

"We made a mistake with the decals, and we take full responsibility for what happened," Mr. Mehdi said in a statement issued by Microsoft's public relations firm, Waggener Edstrom. "We're working with city officials to clean up the decals immediately."

City officials in New York, Chicago and San Francisco have fought back against similar illegal "guerrilla" ad campaigns by IBM, Snapple and Nike.

In April, IBM paid San Francisco $120,000 in fines and cleanup costs for an ad campaign in which sidewalks were spray-painted with ads. Chicago also fined the computer maker for similar corporate graffiti.

In New York, municipal workers removed hundreds of Microsoft decals this week, said Transportation Department spokesman Tom Cocola.

"We intend to hold your firm directly responsible for this illegal, irresponsible and dangerous defacing of public property," Cesar Fernandez, the department's assistant counsel, said in a letter to Microsoft.

Mr. Fernandez said Microsoft could be sued if it sticks more ads on city property.

A public relations spokeswoman for Microsoft, Kathy Gill of the Waggener Edstrom agency, said Thursday that the software company received a city permit to place the blue, green, orange and yellow butterflies on streets and sidewalks.

Ms. Gill didn't say which city agency issued the permit, and Mr. Cocola said the DOT has not seen it.

On Friday, another Microsoft spokeswoman cast doubt on whether the company had permission to post the ads, saying Microsoft was "looking into it."

The decals were part of a splashy promotional campaign for the company's release of an upgraded MSN Internet service stocked with Disney's content.

Many of the decals were clustered on sidewalks near Central Park, where Mr. Gates and Walt Disney Co. chairman Michael Eisner announced the deal Thursday.

"It's a real coup," Mr. Gates said during the kickoff spectacle, flanked by a pair of extras in Mickey and Minnie Mouse suits. Pop star Lenny Kravitz played an invitation-only concert at the event.