Kristian: FYI Cthulu appears to be in the public domain in the EU, the following is from Wikia: "Similarly, the European Union Directive on harmonising the term of copyright protection of 1993 extended the copyrights to 70 years after the author's death. So, all works of Lovecraft published during his lifetime, are to become public domain in all 27 European Union countries on 1 January, 2008."
The same page says his works may also be in the public domain in the US. So I would say the legal risk of someone demanding these games be yanked is probably quite small.
The question is also if they can be said to be external IP games if that IP has been passed on to the public domain?
Yes but, as far as we know, anything that specifically starts 'Call of Cthulhu...' is actually licensed from the table-top roleplaying game
[url=https://en.wikipedia.org/wiki/Call_of_Cthulhu_(role-playing_game]https://en.wikipedia.org/wiki/Call_of_Cthulhu_(role-playing_game[/url])
Quite WHY anyone would pay to license a tabletop role playing system to make a point-and-click adventure when they could use the public domain Cthulhu mythos for free is another question entirely though...