More pernicious forms of activity may also be enabled. For example, a local or international hacker could potentially initiate commands (such as a denial-of-service attack) that could crash the tower software, rendering the tower entirely inoperable to process calls or transmit data. In short, taking control of the BBP software would be much the equivalent of getting inside the firewall of a corporate computer–to potentially catastrophic result.

So claims Apple in their argument against jailbreaking.   Read more from News.com.  Read the full response from Apple.