Today consumers use to buy and get services immediately when they want and need them. Enabling online transactions and mobile transactions is not only a way to monetise and get more customers, but also a real and tangible benefit for people that does not want to lose time in traditional way of payment. A modern payment system unlocks the opportunity of new business models like subscription based services, automatic restock, account sharing and so no. A key aspect of payment services is security, not only related to monetary transactions safety, but also for anti fraud management processes and privacy of historical purchases that can be a very powerful and risky way to profile customers. The purpose of this course is to present basic knowledge of online monetary transactions and security of digital ecosystems.