Technology companies are scrambling to fix a major security flaw that for more than a decade left users of Apple and Google devices vulnerable to hacking when they visited millions of supposedly secure Web sites, including Whitehouse.gov, NSA.gov and FBI.gov. The flaw resulted from a former U.S. government policy that once forbid the export of strong encryption and required that weaker “export-grade” products be shipped to customers in other countries, say the researchers who discovered the problem. These restrictions were lifted in the late 1990s, but the weaker encryption got baked into widely used software that proliferated around the world...