According to a report from German computer scientist D. Kriesel, some Xerox WorkCentre copiers and scanners may alter numbers that appear in scanned documents. Having analyzed the output of two such devices, the Xerox WorkCentre 7535 and 7556, Kriesel found that “patches of the pixel data are randomly replaced in a very subtle and dangerous way”: in particular, some numbers appearing in a document may be replaced by other numbers when it is scanned. These substitutions can be particularly troublesome for documents such as invoices, construction plans, and medical information. Kriesel suspects that the problem may be related to the JBIG2 compression algorithm employed during scanning, which can substitute one scanned region for other scanned regions that are visually similar. So far, no fix has been reported.