The choice of a site for any summit is a complicated issue, and a number of organizations had an interest or a role in that process. It wasn't a security decision as to whether a site was or was not the appropriate venue. Once it was clear that Huntsville was too small to host the G-20—it simply didn't have the infrastructure to do so—the only alternative was to move the G-20 to Toronto, which had the capacity to host and the required infrastructure.
On October 25th, 2010. See this statement in context.