I have just switched the forum marking type from Cookie to Database.
The advantage of this is if you access the forum from other computers such as work, school etc or you delete your browsers cookies the board will now always remember what threads you have or have not read.
Using the database is a much better and more accurate way of displaying new threads, the only downside is after the switch you may now have threads and posts you have read showing up as new.
Once you either read them again, or click the
"Mark Forums Read" link everything will function as normal from that point on.