They also change dimension sizes.
Xerox photocopiers are rewriting documents, experts have discovered.
A German computer scientist found scans he took of construction plans had altered room dimensions from the originals, while the photocopiers also changed numbers on the documents.
Other users allegedly repeated the error, which has been blamed on faults with compression software used by several Xerox models.
Xerox has announced that the issues only occur when scanning and not copying, and then only if users switch from the factory standard default setting, and amend both the resolution and compression settings to lower the quality of a scanned image.
But Kriesel said he worried that numbers on invoices could be altered, and aired the fear that companies could be liable for legalaction due to incorrect figures.
Certain numbers seem to be most commonly affected, with sixes and eights often being swapped round, while dimensions were shrunk by Jbig2, an image compression standard.
Xerox said that it is taking the matter "very seriously’ and suggested users avoid the problem by printing in high resolution until the matter is investigated fully.