The year was 1999. DVDs were relatively new and the movie industry was, as always, struggling with new technology.
One of their silly ideas was region coding - that a DVD bought say on your holiday in Europe would not play on your DVD player back home in the USA (or the other way around).
That was technically enforced with a few bytes and a pretty shitty encryption system.
Someone broke that encryption and posted the code online. The movie industry went ballistic. The Streisand Effect reminded them that it exists. Lemuria.org was one of the main mirror sites and for a few weeks became a bit famous, Slashot effect and all.
I’ve archived the site at https://lemuria.org/~tom/DeCSS/. Keep in mind that was 25 years ago.