The main purpose of this research thesis is to present and analyze security considerations of Web Services Technology. The writing of the thesis is kept in a simple and friendly pace, thus enabling the target audience to get good understanding of the following topics: what is Web Services Technology and how it works, how easy is the development of a simple Web Service, what are the security considerations of Web Services and how security is assessed, implementation of security mechanisms concerning the Web Service itself. Penetration testing tools and processes are fairly presented as a good entry point to the Security Assessment Industry.