U.S. Sen. Joe Lieberman's campaign Web site remained offline, and federal and state authorities were investigating why it crashed on the eve of this week's defeat in a high-profile primary. The site, Joe2006.com, appeared to have suffered from a so-called "denial of service" attack, in which computers overwhelm a site with fake traffic, preventing real visitors from getting through or, in this case, causing it to crash, said Richard M. Smith, an Internet security consultant in Brookline, Mass.