Lexington,Massachusetts,United States

Attackers bent on shutting down large Web sites -- even the operators that run the backbone of the Internet -- are arming themselves with what are effectively vast digital fire hoses capable of overwhelming the world's largest networks, according to a new report on online security.

In these attacks, computer networks are hijacked to form so-called botnets that spray random packets of data in huge streams over the Internet. The deluge of data is meant to bring down Web sites and entire corporate networks.