In case you didn't hear already, 4chan forum was hacked and shut down completely.
Everthing was leaked, including database, emails and IP addresses of members and admins, ban list, and many other things.
I was never a member of 4chan forum, but I did try to register once and I didn't like what I saw.
What can we do to increase security and prevent Bitcointalk suffering something similar in future?
There far many sensitive information in 4chan than Bitcointalk forum which makes 4chan a nice target for hackers. In addition, 4chan have been know to be very controversial in terms of information shared there, which makes government and other agencies have interest in.that platform. Therefore, the security requirements of both platforms may not be the same. Nevertheless it is still important that security be taken seriously. Perhaps, Theymos and his team understand this and only them can tell how secured the forum is.