This refers to sharing files for music, games or other types of software. This sharing requires one to connect with other computers using the same software. This could expose the system to:
The copying of your private files. A hacker is capable of accessing all personal and private information including bank accounts, address and contacts.
Violation of copyright laws. Includes received, downloaded to shared folders/files. The penalty for such a violation is quite harsh.
Incoming viruses that could corrupt data and saving devices permanently and the user might not be aware of the damage already done. Accidentally download pornography that was purposely mislabeled as something else; allowing them to be downloaded to safer websites used for P2P file sharing.