1. A computer system to identify malicious Uniform Resource Locator (URL) data items from a plurality of unscreened data items that have not been previously identified as associated with malicious URLs, the system comprising: one or more computer readable storage devices configured to store one or more software modules including computer executable instructions; and the plurality of unscreened data items associated with communications between computerized devices within a local network and external resources, the unscreened data items comprising a plurality of device identifiers for the computerized devices and a plurality of URLs referencing the external resources; a network connection configured to access, from a remote network not within the local network, a list of domain names satisfying a ranking condition based on Internet traffic data; and one or more hardware computer processors in communication with the one or more computer readable storage devices and configured to execute the one or more software modules in order to cause the computer system to: access, from the one or more computer readable storage devices, the plurality of unscreened data items; identify, from the plurality of unscreened data items, a plurality of connection records, each of the connection records indicating a communication from a computerized device to an external resource at a specific time, such that each of the connection records is associated with a device identifier and a URL, identify, from the plurality of connection records, one or more connection records having a common device identifier, the identified one or more connection records associated with one or more URLs; parse the one or more URLs for one or more domain names, each of the one or more URLs associated with a domain name; based on a determination that none of the one or more domain names satisfies a threshold position in the list of domain names, designate the one or more URLs as possible malicious URL data items; assign a score based on a plurality of factors relating to the possible malicious URL data items, the factors comprising the determination that none of the one or more domain names satisfies the threshold position in the list of domain names.