Detecting malicious tampering of web forms

Telemetry data concerning web pages that users attempt to access containing fields prompting entry of personal information is received from many client computers over time. Based on the telemetry data, it is determined which fields prompting entry of personal information are expected to be present on specific web pages. The fields prompting entry of personal information on web pages users attempt to access are compared to the fields expected to be present. When a specific user attempts to access a specific web page in real-time, it can be adjudicated on-the-fly that the web page is suspicious, based on the web page containing at least one unexpected field. Correlations between web pages containing specific unexpected fields and the hygiene ratings of the users attempting to access the web pages when the unexpected fields are encountered can be tracked and taken into account in the adjudication of web pages.