Security practices in large organizations are notoriously difficult to assess. The challenge only increases when organizations turn to third parties to provide technology and business services, which typically require tight network integration and sharing of confidential data, potentially increasing the organization's attack surface. The security maturity of an organization describes how well it mitigates known risks and responds to new threats. Today, maturity is typically assessed with audits and questionnaires, which are difficult to quantify, lack objectivity, and may not reflect current threats. This paper demonstrates how external measurement of an organization can be used to assess the relative quality of security among organizations. Using a large dataset from BitSight(www.bitsight.com), a cybersecurity ratings company, containing 3.2 billion measurements spanning nearly 37,000 organizations collected during calendar year 2015, we show how per-organizational "risk vectors" can be constructed that may be related to an organization's overall security posture, or maturity. Using statistical analysis, we then study the correlation between the risk vectors and botnet infections. For example, we find that misconfigured TLS services, publicly available unsecured protocols, and the use of peer-to-peer file sharing correlate with organizations that have increased rates of botnet infections. We argue that the methodology used to identify these correlations can easily be applied to other data to provide a growing picture of organizational security using external measurement.