New guidelines are being introduced in the US for companies that supply "custom DNA," in order to guard against bioterrorists looking to build dangerous viruses from the genes up, says the New Scientist. Several firms supply DNA sequences to order, and as the New Scientist reported in 2005, only five out of the 12 that do so in North America and Europe screened every order for sequences that could be used in bioweapons. The new US guidelines state that the companies must verify the identity of buyers and screen orders for dangerous microbes. However, the article adds, the rules are voluntary and don't extend outside the US where a lot of custom DNA is made.