A digital certificate may be extracted from communications between a web browser and a web server computer. The digital certificate may be verified independent of the web browser by comparing the digital certificate against contents of a database containing digital certificates of legitimate websites or by consulting a remotely located security server computer. For example, the digital certificate may be forwarded from a client computer running the web browser to the security server computer. The security server computer may obtain a digital certificate from the web server computer and compare it to the one received from the client computer to detect man-in-the-middle attacks, for example.