This is already happening. For example people steal medical records and use the data to get medical care for themselves and others, pretending to be the identity they have stolen. So false data gets into the medical record and can not by law be removed! So people are getting misdiagnosed due to false information in their medical records. It is very difficult to detect tampering in data, what is the objective truth you can compare to? In many circumstances the data itself is considered the basis of truth. So data tampering could already be widespread and the only time it is detected is when it causes someone problems and then it is likely considered a "computer error".