This thesis deals with data security on the Web, and how to make access to protected data more secure. I wrote this thesis during my internship at IBM, at the Database Technology Institute, in San Jose-California, where I was working in the team Net.Data, which is a dynamic Web page developing tool. I was responsible for all the aspects, which where dealing with the threats on data security on the different parts of the product Net.Data. Computers connected to the Web are exposed to threats, like secrecy, authentication, authorisation, integrity and accountability. After analysing how Net.Data works, I realised that the main threats where on secrecy, authentication and authorisation. • To assure secrecy, I developed a tool for encryption. This tool can be used on ist own, but will also be used in an administration tool for Net.Data with a graphical user interface. • As Net.Data macro files can perform queries in databases, you can think of cases, where certain data should be made available only to authorised users. To assure authentication and authorisation, I extended the code of Net.Data and now only requests from authorised users will be executed. As I was responsible for the data security part, I bad to analyse the requirements and the different possibilities available to reach the target. After designing my solutions, I presented and defended them in front of the whole Net.Data team, to convince my co­workers about the reliability and the level of security of the offered solutions. After the implementation, my code went to the process of code review and only then it was added to a new release of Net.Data. A very interesting point during my internship was to work in an international team, where every member was dealing with the different mentalities, the different cultures and the differnt opinions of the co-workers.