The New York Stock Exchange's three leading indexes fell on Friday, and the broad S&P 500 index thus recorded its worst week since April.
Investors were worried about the IT problems that affected companies and other operations around the world, including airlines and banks. It was an update of a program from the IT security company Crowdstrike that caused Windows computers to stop functioning.
Crowdstrike's share fell sharply when the exchange opened, over 15 percent, but recovered somewhat and closed at minus 11.1 percent. Microsoft, the giant behind the Windows operating system, lost 0.7 percent.
The S&P 500 index fell 0.7 percent, the Dow Jones industrial index fell 0.9 percent, and the technology-heavy Nasdaq composite index lost 0.8 percent. Calculated over the entire past week, the S&P 500 index fell 2.4 percent, while the Dow Jones rose 0.4 percent and the Nasdaq fell 4.1 percent.
