Positive conditions are easier for me to read.

```ruby
if winver =~ /Windows 2000|Windows Vista|Windows 2003|Windows 2008|Windows 7/
  return Exploit::CheckCode::Appears
end

return Exploit::CheckCode::Safe
```

If you still like your version, please switch if with negative condition to unless with positive condition as recommended on the ruby style guide :) https://github.com/bbatsov/ruby-style-guide