Airlines, banks, TV channels and financial institutions were thrown into turmoil on Friday by one of the biggest IT crashes in recent years, caused by an update to an antivirus program.
Microsoft said the issue began on Thursday, affecting Windows users running cybersecurity software CrowdStrike Falcon.
CrowdStrike said it had rolled out a fix for the problem and the firm's boss, George Kurtz, told US news channel CNBC he wanted to "personally apologise to every organisation, every group and every person who has been impacted".
Air passengers crowded into airports to wait for news as dozens of flights were cancelled and operators struggled to keep services on track, after an update to a program operating on Microsoft Windows crashed systems worldwide.