The "Installation Key" for Winfeed 2.8 typically refers to one of two things depending on the version you are using:
For Winfeed 2.8, the demo installation key has historically been provided as wf28-demo-7801-556127 , though this may change. Winfeed 2.8 Installation Key
There is one known keygen floating around from the "CORE" group. It was designed for Winfeed 1.x. Installing it often results in false-positive virus warnings (trojan.agent) because it modifies memory registers to skip the activation check. Do not run these on a modern, networked computer. The "Installation Key" for Winfeed 2