Back in 2002, the Department of Corrections implemented a system at the request of the Washington Supreme Court that would give inmates "good time" credits for participating in rehabilition programs. The credit would knock time off your sentence, but in the 13 years since the program was implemented, an error resulted in some inmates being overcredited which eventually led to the mass release.
Now before anyone starts lecturing about the dangers of overreliance on technology, know that human error plays a part in this. The problem was actually discovered in 2012 but a solution was delayed several times over, leading the state's new chief information officer to alert the DOC to the problem. As far as how early the prisoners were released, the state puts the average time at 49 days, which doesn't seem like too big of a problem.
The state apparently agrees, as not all of the prisoners are being rounded up, and some who are will be given work release opportunities. A software patch designed to fix the error is scheduled for January 7th and two retired federal prosecutors have been hired to investigate why the programming error went unnoticed for 10 years and then unaddressed for three more.
The idea of thousands of inmates being released early thanks to a computer glitch is a lot scarier than what actually happened. I feel as if someone might say "it could have been a lot worse," but in truth it couldn't have been, because all the error really did was speed up a decision that a person had already made. When the computer gets a life of his own and starts swapping prison sentences between low-level offenders and those with multiple death sentences, then we can start panicking.