If you don't know what a magnet link is, click here.
When in a match that is has open slots, a link could be generated that could be sent to a peer. This link would auto-magically launch Intruder with a set of parameters to auto-login, and auto-join that match if at all possible.
Why is this useful?
In the browser extensions, a player could see that there is a server open and join it by only using the extension. The extension would use this "magnet link" in order to launch intruder and join the game. Beyond that, 3rd party websites such as Intruder-DB, could use this to make joining a server even easier.