in reply to hash collision DOS
As far as I can tell from the article, what they have shown is that it is possible to exploit worst case behaviour of hashing algortihms to consume resources and that this exploit can be used against the hashing algortihms in both Perl 5.8.0 and 5.6.1. (And in many other programs)
What happpens when such an attack succeeds is that hash performance goes from O(n) to O(n^2). This matters a lot if n is several tens of thousands, but not at all if n is around 10 or 100. You can exploit this if (and only if) you can send large amounts of data to a program which then gets stored in a hash in the program.
To fix this you just need to patch perl to use a different hashing algorithm. I leave this as an exercise for you...