`$map` is an inappropriate use of global variables; I think you forgot this one.  Instead have `Server` create an instance of `Map`.

Or, better yet, just move the `MAP` definition from class `Map` to `Server` and not have the `Map` class at all.  I don't think it buys you anything.  Then `#computer_id` will simply become:

```ruby
def computer_id(paypal_id)
  MAP[paypal_id]
end
```