having OS security patches doesn't mean you can be hacked while firewalled. Mostly these vulnerabilities happen under a very specific scenario, mostly requiring you to visit a malicious website or use a specific application/setting.
Yes, and many hackers have a tool bag of exploits they can execute at their disposal when one fails.
How do you hack 51 delegate's private computer without knowing their IP address, even assuming their computer all have vulnerabilities?
Their are many ways to hack the delegates without knowing any IP addresses: phishing attacks , creating malicious sites or landing pages that exploit 0 day vulnerabilities in java/javascript/flash/pdf/ect..., finding a flaw within bitshares itself, and how about starting by targeting these people:
http://bitshares.org/community/team/All one has to do is compromise one of them and the rest are easily compromised afterwards.