The code you posted is a classic example of a fork bomb. It's a malicious code that can cause serious damage to a computer system.

Here's what it does:

The first part `:(){}` defines a function named `:`. The function is empty, so it doesn't do anything.

The second part `:|:&` is where the magic happens. It calls the function `:` recursively, which creates a new process that calls the function again, and so on. This creates an exponential growth in the number of processes running on the system, eventually causing the system to crash or freeze.

The `|` symbol pipes the output of the function to another instance of the function, and the `&` symbol sends the process to the background, allowing the function to be called again without waiting for the previous instance to finish.

The final `;:` calls the function once to start the process.