A computer system is provided. The computer system includes a memory and at least one processor coupled to the memory and configured to protect against theft of user credentials. The at least one processor is further configured to recognize a uniform resource locator (URL) to which a web browser is navigating, as a URL for which protection is to be provided. The recognition is based on an absence of the URL from a history of visited URLs for which a password has been entered. The at least one processor is further configured to extract a character sequence of selected length that is entered into a field of a website associated with the recognized URL; compare an encryption of the character sequence to entries in a list of encrypted partial passwords of the same selected length; and perform a security action in response to a match resulting from the comparison.