The breach itself remains mysterious and there are not any definitive theories that have approached a complete breakdown of how this breach occurred. Ngak (2013) proposed that "A hacking group going by the name of the Syrian Electric Army has claimed that they are responsible for the breaches. Typically, the hackers spread political messages and misinformation."

No real concrete data has been gathered about this group and has not been confirmed as well. Either way, he blames Twitter and its password systems for many of these hacking problems. He continued "Twitter's lack of two-step authentication. Verified accounts -- those belonging to famous people or organizations to which Twitter adds a check mark because of the volume of parody accounts -- are particularly in need of this. As we saw from Tuesday's event, just one tweet can affect global financial markets."

Most importantly, the question remains how did this happen? The AP's Twitter account represents the breach point of this operation and all investigations must begin at that point. Specifically, passwords can be cracked by many different methods and the need for a back up authorization barrier seems that it may have prevented this security breach.

Bloomberg (2013)...

The article wrote "Paul Colford, a spokesman for the AP, said the hacking incident was preceded by a "phishing" attempt on the AP's corporate email network. Employees had been sent emails with malicious links or attachments that, once clicked, would give an attacker a foothold." In other words, someone internally from the AP was infiltrated through a spam or phishing technique that allowed the hackers to gain the Twitter password.
Data Flow Diagram

References

Greenfield, R. (2013). Look What the Hacked AP Tweet About White House Bombs Did to the Market. Atlantic Wire, 23, Apr 2013. Retrieved from http://www.theatlanticwire.com/technology/2013/04/hacked-ap-tweet-white-house-bombs-stock-market/64492/

BloombergNews (2013).How did AP's Twitter Account get Hacked? Bloomberg News, 24 April 2013. Retrieved from http://www.tampabay.com/news/nation/how-did-aps-twitter-account-get-hacked/2117089

Ngak, C. (2013). Security pro-on Twitter hacks: No patch for human error. CBS News 24 Apr 2013. Retrieved from http://www.cbsnews.com/8301-205_162-57581160/security-pro-on-twitter-hacks-no-patch-for-human-error/