Threat analysis of a web application can lead to a wide variety of identified threats. Some of these threats will be very specific to the application; others will be more related to the underlying infrastructural software, such as the web or application servers, the database, the directory server and so forth. This paper analyzes the threats that can be related to the use of web services technology in a web application. It is part of a series of papers, written by different academic teams, that each focus on one particular technological building block for web applications.