According to an aspect of this invention, a method to detect phishing URLs involves: creating a whitelist of URLs using a first regular expression; creating a blacklist of URLs using a second regular expression; comparing a URL to the whitelist; and if the URL is not on the whitelist, comparing the URL to the blacklist. False negatives and positives may be avoided by classifying Internet domain names for the target organization as “legitimate”. This classification leaves a filtered set of URLs with unknown domain names which may be more closely examined to detect a potential phishing URL. Valid domain names may be classified without end-user participation.