Why don't big companies keep their computer systems up-to-date?

Douglas C. Schmidt, Ph.D., is an Electrical Engineering and Computer Science Professor, the Associate Chair of Computer Science and Engineering, and a Senior Researcher at the Institute for Software Integrated Systems, at Vanderbilt University. The Equifax hack exposed 143 million people’s personal data to unknown cybercriminals starting in March and wasn’t made public until mid-September. Doug Schmidt believes that this attack was entirely avoidable because Equifax, like many other big companies, was using out-of-date software that made them even more vulnerable.