Something like a chan has to realize it WILL be hacked. Users of chans need to realize their favorite chan WILL be hacked. The only defense against this is
High importance:
1) Users: Do not give sufficient data to the chan to know who you are
2) Chans: Do not force users or jannies to give sufficient data to the chan to know who they are
Medium importance
3) Chans: make hacking the chan hard
4) Users: don't be a leech. If possible, give back anonymously
Low importance
5) Chans: do not store unnecessary data ( users can't know if you are which is why this is not important. Users should expect you to do this, however not having data means you can't be ordered to hand it over and makes you less of a hacking target )
6) Chans: secure the data you have.