What is Skynet?
1.
Today it's called
The
With the numerous security flaws in Microsoft's products, a hacker can easily create bugs which will guide Microsoft Windows into becoming a self-aware, Skynet-like system.
See
2.
A military AI computer network created by Cyberdyne Systems that gains sentience and begins a genocidal war against humanity when US military officials try to pull the plug on the project. Sends two Terminators back in time, one to destroy opposition leader John Connor's mother before Connor is born, and one to eliminate Connor ten years later.
Skynet's undoing was its use of humans to dispose of bodies in its death camps.
3.
Artificial Intelligence in the Terminator movies that inevitably becomes sentient. It is more real than people could possibly imagine. The military doesn't call it AI, though. They call it C³I which is short for Command Control and Communications Intelligence. The Star Wars program is part of Skynet.
Terminators might be science fiction, but Skynet is not. Skynet is closer than you think.