gnus-check-bogus-newsgroups

gnus-check-bogus-newsgroups is a variable defined in `gnus-start.el'.
Its value is

nil

Documentation:
*Non-nil means that Gnus will check and remove bogus newsgroup at startup.
If this variable is nil, then you have to tell Gnus explicitly to
check for bogus newsgroups with b.

You can customize this variable.