Hello everyone,
There was an fatal error, when connecting to any server, caused by an error during the network initialization. This bug should now be fixed.
(Note: The game still does only support local LAN multiplayer. Playing over the internet requires third party programs, which emulate a local network like hamachi or tunngle. Unfortuantely not all games (including this one) work with those programs right away, please try the trouble shooting guides of those programs when encountering "Invalid IP" error from Intruder Alert first.)
Greets knittely
P.S. For those who used the temporary workaround, the "multiplayer" BETA branch does now not exist anymore
UPDATE 18.02.2018: there was still a small mistake with the multiplayer code, although it shouldn't have caused any bugs. I fixed it anways, since some people still got some errors.