Even though it was a relatively quiet week in terms of economic data pertaining to the U.S., all of the major indexes posted healthy gains. Similar to two weeks ago, the Nasdaq was the best performer, gaining 1.71%, or 57 points, over the past five trading sessions, and while the S&P 500 and the Dow Jones Industrial Average (^DJI -0.11%) surpassed their milestones during the previous week, the technology-heavy index broke the 3,400 barrier this week. While the S&P rose higher by 1.19%, the blue-chip index increased by 144 points, or 0.96%, and now sits at the all-time high closing price of 15,118.

Before we hit the Dow losers, let's look at the big winner of the week. UnitedHealth Group (UNH 0.23%) shares rose by 6.77% despite falling as much as 1.26% on Thursday. The main catalyst this past week came on Wednesday, when the White House released a mountain of data showing the massive inconsistences within the health-care industry. Investors cheered the news, because some believe the different prices charged by different hospitals throughout the country for the same procedure will soon be a thing of the past, a move that should help the insurance companies through lower payouts.  

The big losers
In a surprising turn of events, shares of Microsoft (MSFT 0.37%) ended this past week lower by 2.64%, after being the best-performing Dow component the prior week, gaining 5.34%. Not only that, but this was also the first-full week loss shares posted since the third week of February.

This past week, the company announced that it's again going to guarantee revenue for ads appearing on Yahoo! websites. Microsoft and Yahoo! have been involved in a search partnership for a number of years now and have previously had a per-search revenue guarantee. So while this announcement may not be something investors liked reading about, it shouldn't have been a shock to anyone.

Also this week, the European Union agreed to hear Cisco's appeal against Microsoft's acquisition of Skype Technologies. Cisco claims the EU should have placed restrictions on the terms of the $8.5 billion buyout in which Microsoft would be required to open Skype's platform to rivals' products and allow them to work with the video technology.  

But the Dow component that ended the week as the biggest loser was McDonald's (MCD -0.05%), after shares fell 2.64%. Investors began selling off shares after the company released April sales figures. Although revenue increased in the U.S. market by 0.7%, globally sales fell 0.6% during the month. The company saw the largest decline in the European market, where sales fell 2.4%. Management, not wanting to waste a great scapegoat opportunity, even threw in the avian flu outbreak in China as one reason the monthly numbers were disappointing.  

Meanwhile, after falling 3.75% and making the Dow's biggest-losers list two weeks ago, shares of Pfizer (PFE -0.19%) again moved lower this past week. While the previous drop came on the heels of disappointing earnings reports from both Pfizer and some of its peers, this week's decline can't necessarily be blamed on anyone but the company itself. Not only did Pfizer go ex-dividend on Wednesday, but the poor earnings report, in which the company missed on both the top and bottom line, was probably still also exerting a hangover effect on the shares. As a whole, the week was rather news-free when it came to negative announcements pertaining to Pfizer, even as the stock lost 0.83% of its value during the past five days.

Other Dow losers this week: