The Gibson Research Corporation (GRC) port scanner web site is one of
the best sites available for getting a thorough and informative test of
how well your computer is protected (firewalled) from internet threats.
The creator of the site, Steve Gibson, was one of the earliest and most
adamant critics of the dangers from defaults setting in Windows that
exposed the identity of local computers and printers on the Internet.
The rise of automated botnets that exploit even the tiniest security
holes tend to confirm many of Mr Gibson's early concerns.