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.
I am not really familiar with the 4chan forum, but with my little findings about what the 4chan forum looks like, I am made to understand that the forum is not well moderated, anyone whether registered or not can come in and post some random unfiltered contents without much moderation from the moderators. If this fact about the 4chan forum is true, then no one should be surprised such an attack and damage could be done to that forum that easily.
I am not bothered about such happening to Bitcointalk. The forum administrators, moderators and every member of this forum have been very active in taking care of some unusual activities in this forum. There is really nothing much we can do aside reporting suspicious activities and I believe the administrators of this forum are not relaxed when it comes to the security of the forum.