In an embodiment, a computing system, such as a monitoring computer, receives a request from a user to monitor an account of the user with an online service provider. The request may include personal information and user preferences for one or more protective actions. The system periodically monitors external data sources for indications of changes to personal information associated with the account, and detects changes or attempted changes to personal information associated with the account. The system may determine risk levels associated with detected changes or attempted changes, and transmit a notification to the user via a communication channel selected based on the determined risk level and/or the user preferences. The system may also initiate protective actions, so that further unauthorized access to the account may be prevented.