Duo Security

Duo Security, now part of Cisco, is a cloud-based identity security platform that verifies who is requesting access to an application and whether the device they are using can be trusted. Its best-known component is multi-factor authentication, delivered through a mobile app that sends a push notification the user simply approves or denies, alongside alternatives including passcodes, hardware tokens, biometrics and phone callback for users without smartphones. The push-based approach is largely responsible for the product's adoption: it removes the friction of typing codes, which historically was the main reason MFA rollouts stalled against user resistance. Duo protects access to cloud applications, on-premises systems, VPNs, remote desktop, SSH and custom internal applications, and it is designed to deploy quickly across an existing estate rather than requiring a re-architecture of identity infrastructure.

Beyond authentication, the platform implements the core of a zero-trust access model. Device trust checks the security posture of every endpoint at the moment of access — operating system version, patch level, disk encryption, screen lock, presence of endpoint protection, whether the device is corporate-managed or personal — and blocks or warns when a device falls below policy. Adaptive access policies combine that signal with user role, location, network, and risk indicators such as impossible travel or an unfamiliar device, so low-risk sessions pass through with minimal friction while anomalous ones face additional verification or denial. Single sign-on and passwordless authentication reduce credential exposure further, and administrators get a detailed inventory of every device touching corporate applications, which for many organisations is the first accurate picture they have had. Reporting and logging support compliance requirements across frameworks such as HIPAA, PCI DSS and SOC 2. Duo is used across organisations of every size, with particular strength in higher education, healthcare and mid-market enterprises. Pricing starts from around USD 3 per user per month with a free trial available and no free version indicated in this listing.