Yahoo Inc. delivered first-quarter results that surpassed analysts' modest expectations, but the performance might not be enough to fortify the Internet pioneer's defense against Microsoft Corp.'s takeover bid.

The company said Tuesday that it earned $542.2 million, or 37 cents per share, more than tripling from its profit of $142.4 million, or 10 cents per share, at the same time last year.

Most of the first-quarter improvement stemmed from a one-time gain of $401 million generated by Yahoo's stake in the parent company of Alibaba.com, a leading e-commerce site in China.

If not for the Alibaba windfall, Yahoo would have earned 11 cents per share - comparable to its profit at the same time last year, on an apples-to-apples basis.

After subtracting commissions paid to Yahoo's advertising partners, the revenue totaled $1.35 billion - just $30 million ahead of analysts' average projection.

Perhaps even more importantly, Yahoo didn't raise its revenue outlook for the remainder of year.

That could be good news for Microsoft, which has been betting that its takeover bid would become irresistible if Yahoo can't substantially accelerate its growth amid the decaying U.S. economy.

DuPont

The chemicals company said profits increased 26 percent in the first quarter, as strong sales of farming chemicals and seeds and brisk business overseas offset a slowdown in the U.S. economy.

DuPont reported earnings of $1.19 billion, or $1.31 per share, up from $945 million, or $1.01, a year earlier. Sales grew 9 percent, to $8.6 billion, thanks largely to higher local selling prices and the weak dollar. The favorable currency exchange offset a 1 percent decline in overall volume. Revenue totaled $8.77 billion, up from $8.16 billion.

McDonald's

Strong international sales helped the fast-food giant post a 24 percent gain in first-quarter profit, but investors seemed nervous about the company's first monthly decline of U.S. same-store sales in five years.

The company easily topped Wall Street forecasts by earning $946.1 million, or 81 cents per share, up from $762.4 million, or 62 cents per share, during the same period last year. Revenue climbed 6 percent, to $5.6 billion.

AT&T

Showing few signs of being affected by a slowing economy, the company's first-quarter earnings rose 22 percent on strong growth in wireless. The wireless division at country's largest telecommunications company continued to drive growth, even as the local-phone business is stuck with declining numbers. AT&T earned $3.46 billion, or 57 cents per share, compared with $2.85 billion, or 45 cents per share, a year ago. Revenue rose 6.1 percent, to $30.7 billion.

UnitedHealth Group

The insurer said first-quarter profits rose 7 percent, missing Wall Street expectations, and it slashed its full-year profit outlook in part because of a drop-off in corporate customers.

UnitedHealth earned $994 million, or 78 cents per share, up from $927 million, or 66 cents per share, during the same period last year. Revenue rose 7 percent, to $20.30 billion.

Yum Brands

The fast-food company reported a 31 percent jump in first-quarter profit because of robust growth in its China and international divisions. The parent of Taco Bell, KFC and Pizza Hut also raised its full-year earnings forecast and said net income rose to $254 million from $194 million in the year-ago period, beating analysts' estimates.