RC4

The earliest Wi-Fi security standard was something called WEP, which stands for Wired Equivalent Privacy, and it represented the first attempt to secure wireless networks with encryption.

WEP used a simple encryption algorithm called RC4, which was state-of-the-art when Wi-Fi first emerged.

But over time, security researchers discovered fundamental flaws in how WEP implemented this encryption.

The algorithm could be broken relatively quickly with the right tools, and by the early 2000s, WEP was considered compromised.