In the past, security breaches were viewed as a single event occurring at a certain point in time. However, this is no longer the case. Security threats now rarely occur as singular events, and a new kind of attack is on the rise: Advanced Persistent Threats (APTs). An APT is a network attack in which an unauthorized person or device gains access to a network and, instead of immediately stealing data or damaging infrastructure, stays there for a long period of time, remaining undetected. It could even occur from a device or person with proper security clearance, thus appearing as normal activity. It is much harder to detect these attacks as they are typically small in scope and focus on very specific targets (usually in nontechnical departments where security threats are less likely to be noticed or reported), and occur over a period of weeks or even months.

In 2014, RSA, a cybersecurity company was called into the U.S. government’s Office of Personnel Management to fix a low-level problem. Upon arrival, RSA discovered that there were intruders in the company’s network, and they had been there for over 6 months routinely stealing data in an organized yet inconspicuous manner. If not for the coincidental security check from RSA, the organization would have never noticed the breach. Ironically, the door into the system was unwittingly opened by an employee who accidentally downloaded malware from a spearphishing attack, much like the google docs cyber attack that took place in May. The employee was quickly informed and asked to change his password: he and his company thought the breach ended there, but it continued for months undetected.

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http://www.enaxisconsulting.com/big-data-drawing-insight-from-security-breaches-blog/