Thanks to Tim bug 550 is fixt and now it is possible to be more specific who and what you like to block.
To specify this there are 2 tick boxes with these default settings;
[ ] Block anonymous users only
[X] Prevent account creation
I find these are not good default settings. The default setting should be the softest block possible. And that is only a block for anonymous users and account creation allowed.
So that this would be the default setting;
[X] Block anonymous users only
[ ] Prevent account creation
Can this be specified somewhere by a sysop on the wiki?