Thank you for the link. I have read the letter and I am taking it with a grain of salt. 
While the group VIPS may have been right in 2003 regarding WMD, it does not mean they are necessarily right this time regarding the hacking. WMD and hacking are two totally different and unrelated issues. Furthermore, I would expect the composition of the VIPS group will have changed since 2003. Also, that the signatories of the letter were intelligence officers does not make them experts in hacking technology, and I have no idea of what their qualifications are to write such report with authority and credibility.
But rest assured that if the contents of the letter have any traction we will hear of it in the MSM during the next days or weeks.