Bioterrorism has been in the minds of millions of Americans ever since the 'anthrax letters' were sent just after 9/11. Unlike conventional terrorism, where a bomb blast is a clear sign that something has happened, biowarfare methods such as spraying viruses into the air or polluting water sources are silent and often leave no visible trace. How do we know if something has happened, and, more importantly, what do we do about it? Israeli scientists are coming up with answers from several different angles.