We have chosen to look closer at the area of security for electronic invoices. The purpose of this inquest is to provide our case study with a security analysis of three suggestions and a recommendation of the best solution, according to our test. The three solutions are ISDN via a third party, X.25 via Internet bank and Mail server. The company in our case study is in this report referred to as X, has a strong market position and a large clientele and therefore we were interested in analysing and improving X?s electronic invoice system. X was in the position of testing an electronic invoicing system towards a selective group of business customers. The major problem with the system was the security issue regarding transferring the file.