We have standalone installs of QuickBooks 2012 and QuickBooks 2013. Whenever the update would run on either, QuickBooks would consume 100% of our bandwidth, saturating our internet and causing major issues.
In addition to this, the updates would take hours to complete - odd given that they were consuming so much bandwidth (we have 30mbps fiber). If that copy of QuickBooks were taken off of our network - the update would complete in minutes.
We are running a Barracuda Web Filter 310 inline between our network and firewall (a Cisco ASA 5510). Turning off content caching (Advanced > Caching > Enable Content Cache) resolved the issue. The same QuickBooks update that saturated our internet and took hours was now only a few minutes long.