[Logician]

In newreply.php and newthread.php, find

$message=trim($message);

after that add:

$message=ereg_replace('[\n]+',"\n",$message);

This will convert all consecutive new lines to a single new line.

However I dont think this will stop your users as easily as you thought. They can just use:

.
.
.
.
.
.
.
.

Or if you stop this, there can be always imaginative members using this method which is impossible to be stopped by a hack:
s
c
r
o
l
l

m
e

n
o
w

See? Maybe you should regard warning the users instead of trying to stop them via a hack. My 2 cents..

Regards,
Logician