Computer pioneer Fernando Corbato, who first used passwords to protect user accounts, has died aged 93.
Dr Corbato introduced the basic security measure while developing methods that let more people use a computer at the same time.
He developed a technique, called time-sharing, that divided up the processing power of a computer so it could serve more than one person at once.
Dr Corbato reportedly died as a result of complications caused by diabetes.
The work on sharing a computer was done at the Massachusetts Institute of Technology (MIT), where Dr Corbato spent his entire career.
He joined MIT in 1950 to study for a doctorate in physics, but realised during those years that he was more interested in the machines that physicists used to do their calculations than in the subject itself.
Using computers during the 50s was an exercise in frustration because the huge, monolithic machines could only handle one processing job at a time.
In a bid to overcome this limitation, Dr Corbato developed an operating system for computers called the Compatible Time-Sharing System (CTSS).
Rather than have the machine dedicated to one person, CTSS divided up the processing power of a computer into small slices so it could do little bits of work for lots of people.