1. A method comprising: storing, at a computer system executing a monitor that lacks access to confidential data having a tabular structure, an index derived from the confidential data, wherein the index defines the tabular structure of the confidential data; receiving, by the monitor, information content; detecting, by the monitor, in the information content, a sequence of content fragments that is indicative of containing a portion of the confidential data without using the index and without accessing the confidential data having the tabular structure; in response to detecting the sequence of content fragments that is indicative of containing a portion of the confidential data, determining by the monitor whether a subset of content fragments within the sequence matches any sub-set of the confidential data using the index derived from the confidential data without accessing the confidential data having the tabular structure; and performing a data loss prevention action based on results of determining whether a subset of content fragments within the sequence matches any sub-set of the confidential data.