Making subtle genetic alterations to existing pathogens to increase their virulence or durability in the environment, or to make them more difficult to detect or to treat with drugs is within the limits of today's technology. One disturbing possibility is that knowledge of pathogen genomics could be combined with insights gleaned from human genetics to target particular ethnic groups, but most experts are skeptical of the potential for bioweapons as agents of "ethnic cleansing." The accumulation of genomic and other biological data is also spawning a boom in computational biology, which uses mathematical modeling to help understand how networks of genes and proteins work. Although such approaches might yield information on drug targets, they could also highlight vulnerabilities that could be exploited by malevolent biologists. Other approaches that might be used to develop bioweapons include the deliberate hybridization of related viral strains. Potential bioweapons designers might also find ways to ferry harmful genes into unsuspecting victims. Researchers working on biological defense take the threat of bioengineered weapons seriously, and they are attempting to develop the means to counter it. Sandia's Center for National Security and Arms Control is developing an Internet-based system to detect early signs of bioweapon exposure, irrespective of the agent responsible. In collaboration with the Lawrence Livermore National Laboratory in California, Sandia is also attempting to develop generic methods to detect biological agents without needing to know their identity. The U.S. Defense Advanced Research Projects Agency is developing biosensors based on living tissues that should provide physiological responses to a wide spectrum of both known and unknown pathogens. This agency is also investing in the development of new antibiotics and vaccines that could target a broad range of pathogens. Thus, the techniques that could produce bioweapons are also being deployed to develop countermeasures. 15 notes