Microsoft and Mozilla have acknowledged that <A HREF="http://news.zdnet.com/2100-1009_22-6081828.html?tag=zdnn.alert">a security hole in their Web browsers</A> could let an intruder nab files, but say it is tough to exploit and so not that high a risk. Internet Explorer and Firefox, as well as other Mozilla browsers, are flawed in the way they handle JavaScript, security experts warned this week. An attacker could use the problem to launch surreptitious file uploads, jeopardizing people's personal data, they said. But exploiting the flaw requires so much user interaction that Microsoft and Mozilla don't think it poses much of a danger.