test.rb

mark@Marks-MacBook-Air ~$ cat test.rb 
class Klass

  attr_accessor :business
  private :business=

  def apps
    self.business ||= 1
  end

end

puts Klass.new.apps
mark@Marks-MacBook-Air ~$ rbenv global 1.8.7-p370 && rbenv rehash 
mark@Marks-MacBook-Air ~$ ruby test.rb
1
mark@Marks-MacBook-Air ~$ rbenv global 1.9.3-p286 && rbenv rehash 
mark@Marks-MacBook-Air ~$ ruby test.rb
test.rb:7:in `apps': private method `business=' called for #<Klass:0x007fbbbbed7e88> (NoMethodError)
  from test.rb:12:in `<main>'
mark@Marks-MacBook-Air ~$