The second largest European IT-related conference is FOSDEM (5000 participants); of course it has a different focus. But it&#x27;s more productivity, less party.<p>Then there are conferences like HITB Sec Conf that are much smaller, but focus exclusively on security - many (probably most) Congress attendees don&#x27;t really have a security&#x2F;hacking background, so I&#x27;m not sure the total number of attendees is a good metric for &quot;is it a good security conference?&quot;.<p>Though Congress <i>does</i> get all the high-profile talks. And there is no European hacker conference with nearly as much visibility as C3.