1. A data leak prevention system, comprising: a client device; an application resident on the client device, the application having source code that is unavailable or non-modifiable; a system call emittable by the application as a result of an action that is able to export a document out of the client device, the system call to take place before a data leak event can occur, and the action involving the document and i) latest full contents of the document, ii) metadata of the document, or iii) a combination of the latest full contents and the metadata; a system call interceptor agent resident on the client device, the system call interceptor agent including a system call interceptor to intercept the system call emitted by the application and to suspend the system call; and a policy decision engine to perform a deep scan, according to a policy condition, of at least some of i) the latest full contents of the document, ii) the metadata of the document, or iii) the combination of the latest full contents and the metadata to determine a real-time document sensitivity and to determine whether a policy applies to the document that is attempted to be exported out of the client device, and implement a policy action based upon the real-time document sensitivity.