...virus that erased files and overwrote Web pages. Sharon Ruckman, senior director at San Francisco-based Symantec Security Response, calls the latest intruders, such as Nimda, "integrated security threats." "They're more than just...

...millions of others. "It's definitely a growing concern," said David Loomstein, group product manager with Symantec Security Response, which monitors online threats. Loomstein estimates that there are 3,000 to 15,000 malware threats floating...