The computerized attack that left more than 1,200 websites unreachable on Friday stemmed from efforts, years earlier, by players of online games to frustrate and slow their opponents, security experts say.

The massive denial-of-service attack was launched from thousands of internet-connected devices, including cameras, video recorders and routers. It overwhelmed computer servers at Dynamic Network Services Inc., also known as Dyn, which plays a crucial role in connecting users to websites. Popular sites including Twitter Inc.TWTR, +7.04%   and Netflix Inc. NFLX, +3.36%   were unreachable for parts of Friday.

On Saturday, Dyn said the attack had ended, though it continued to investigate the causes.

Several security experts say the computer instructions for the attack had been refined from code written by disaffected videogame players calling themselves Lizard Squad who launched attacks on Christmas Day 2014 against online-game services operated by Sony Corp. SNE, -1.86%   and Microsoft Corp. MSFT, +4.21%

Since then, the experts said, the code and hacking techniques have been passed around and made more powerful. Friday’s attackers used it to seize control of devices connected to the internet, many with weak security, and assemble them into an online army, or “botnet.” Both the code, and the botnet, used in Friday’s attack are called “Mirai.”

[Source:-Market Watch]