This kept legitimate users from logging on or even crashed the site. Common sense and good network hygiene will go a long toward reducing the impact of large-scale attacks but won't eliminate the chances they will occur. That includes outbound packet filtering, so that systems don't become a zombie launchpad to attack other sites, he says. The truly prepared will run many duplicate sites, because it's unlikely that an attack will concurrently cripple all servers at once. There's no magic to keeping businesses safe and virus-free.
Experts agree it's a matter of knowledge, diligence, and a bit of luck.