During investigative activities in the field of contrasting tax evasion and fraud, it is known that law enforcement agencies are increasingly encountering digital documents, which are slowly replacing the paper ones. The chapter has the purpose to explain as data, extracted from an electronic device, turns into evidence in court. The authors describe how hidden data (metadata) can become forensic evidence. In particular, the chapter examines the metadata contained in digital photos, which conceal a mass of data whose existence is not normally suspected. The second part of the chapter consists of miscellaneous cyber-attack descriptions in which computer forensics can be applied. It is finally described how one can protect systems against a cyber-attacks.