prohibits the creation and distribution of indecent images of children. This concern may delay the introduction of routine backscatter scanning in UK airports, which had been planned in response to the attempted Christmas Day 2009 attack on Northwest Airlines Flight 253. The Fiqh Council of North America have also issued the following fatwa in relation to full-body scanners: In August 2010, it was reported that U.S. Marshals (part of the Department of Justice), saved thousands of images from a low resolution mm wave scanner: This machine does not show details of human anatomy, and is a different kind of machine from the one used in airports. TSA, part of the Department of Homeland Security, said that its scanners do not save images and that the scanners do not have the capability to save images when they are installed in airports, but later admitted that the scanners are required to be capable of saving images for the purpose of evaluation, training and testing. Health risks Unlike cell phone signals, or millimeter-wave scanners, the energy being emitted by a backscatter X-ray is a type of ionizing radiation that breaks chemical bonds. Ionizing radiation is considered carcinogenic even in very small doses but at the doses used in airport scanners this effect is believed to be negligible for an individual. If 1 million people were exposed to 520 scans in one year, one study estimated that roughly four additional cancers would occur due to the scanner, in contrast to the 600 additional cancers that would occur from the higher levels of radiation during flight. Since the scanners do not have a medical purpose, the United States Food and Drug Administration (FDA) does not need to subject them to the same safety evaluations as medical X-rays. However, the FDA has created a webpage comparing known estimates of the radiation from backscatter X-ray body scanners to that of other known sources, which cites various reasons they deem the technology to be safe. Four professors at the University of California, San Francisco, among them members of NAS and an expert in cancer and imaging, in an April 2010 letter to the presidential science and technology advisor raised several concerns about the validity of the indirect comparisons the Food and Drug Administration used in evaluating the safety of backscatter x-ray machines. They argued that the effective dose is higher than claimed by the TSA and the body