Bungie is preparing for the launch of their biggest expansion yet, The Taken King, and part of that preparation is Patch 2.0. While many of the changes coming with patch 2.0 were known, there was much speculation over how the weapons of Destiny would be effected. Turns out the effect will be massive, with almost all of the games weapons being changed in some way, including the game's top guns like Thorn and Gjallahorn.

In the very detailed and thorough news post, Sandbox Designer Jon Weisnewski laid out the changes to every single wepaon in the game in detial, along with the how they came to the decision. If you're an avid Destiny player you will definitely want to check it out. Here is a sample from the document that goes over the thoughts behind the changes to the Thorn hand cannon.

We want to preserve the functionality that makes Thorn such a compelling weapon, but its effective range and lethality are one of the most hotly contended items by the PVP player base. The base changes to Hand Cannons and weapon stats address Thorn’s range.
Changes:

• Reduce base damage of Thorn’s Mark of the Devourer DoT (Damage over Time) to roughly 1/3 of what it was in PVP and PVE
• Allow DoT to stack up to 5x across multiple landed projectiles

This is a net buff for Thorn’s DoT, but reduces the lethality of the weapon in PVP