Phishing attacks generally rely on a number of simple tools and techniques to trick unsuspecting users. The underlying infrastructure to support a phishing scam may be as basic as a simple copied HTML page uploaded to a freshly compromised web server and a server side script to process any user input data, or it may involve more complex web sites and content redirection, but generally the objectives are the same - to set up a fake web presence for a trusted brand with the necessary back end capabilities to process user input data and make it available to the attacker. Using modern HTML editing tools it is very easy to produce a web site mimicking a target organisation, and poorly secured web servers can easily be located and compromised if an attacker is not adverse to scanning entire portions of Internet IP address space in the search for vulnerable target hosts. Once compromised, even home PCs can make effective hosts for phishing web sites, so not only well known corporate or academic systems are targeted. Attackers are often indiscriminate in their choice of target computers, purely selecting large IP address blocks to scan at random for a particular exploitable security vulnerability.
Once a phisher has established a realistic and convincing fake web site that mimics a trusted brand, their main challenge is how to divert users of a legitimate web site to the fake web site instead. Unless the phisher has the ability to alter the DNS for a target web site (DNS poisoning) or somehow otherwise redirect network traffic (a technique sometimes referred to as pharming), they must instead rely on some form of content level trickery to lure unfortunate users to the fake web site. The better the quality of the lure, and the wider the net that can be thrown, the greater the chance of an innocent user mistakenly accessing the fake web site (and in the process potentially providing the phisher with the victim's credentials or other personal data).
Unfortunately for the attacker, when they target an individual organisation (such as a bank or trusted retailer), the phisher probably does not have any information about who on the Internet is a customer of the target organisation and therefore who might be most receptive to a particular lure. Although the attacker could post hyperlinks pointing to the fake web site on chat rooms and forums related to the target brand (such as a technical support web site or community discussion group), it is likely that the target organisation would be notified reasonably quickly and the offending hyperlinks removed or discredited before many victims had accessed the content and submitted their personal details. There would also be a significant risk that the target organisation or law enforcement agencies might trace and potentially shut down the fake web site. The phisher therefore requires a method of reaching the maximum number of potential victims with the minimum amount of risk, and they have found their ideal partner in crime in the form of spam email.
Spammers have databases containing many millions of active email addresses, so the latest mass emailing techniques can be employed to allow a phisher to distribute their lure to a very wide audience with very low risk. Spam emails are often sent via compromised servers hosted in foreign countries, or via global networks of zombie PCs (botnets), so the likelihood of an individual sender being traced is low. If an unsuspecting user receives an officially branded email that appears to have been sent by their bank which asks them to go to what appears to be the bank's usual branded web site to change their online banking password for security reasons, they are much more likely to consider doing so than when confronted with standard spam emails about novelty products and links to unknown web sites. To increase the likelihood that a user will believe that an email is genuine, the phisher can employ a number of techniques to further improve the quality of their attempted deception:
Due to the relatively complex nature of many e-commerce or online banking applications, which often employ HTML frames and sub-frames or other complex page structures, it may be difficult for an end user to easily determine if a particular web page is legitimate or not. A combination of the techniques listed above may mask the true source of a rendered web page and an unsuspecting user might be tricked into mistakenly accessing the phisher's fake web site, unknowingly divulging their authentication credentials or other personal data. At this point the phisher will be free to make use of the user's accounts or electronic identity as required, and the user becomes another victim of a successful phishing attack.