A file attached to an email as an enclosure. Most email programs make it easy to send file attachments containing photos, documents, music and videos. Simply select Attach from the menu then use Browse to find the right file to send. Note that the file size may increase by up to 30%, as the email program encodes the file attachment before it is sent and after it is received. Caution is also advised if one doesn’t recognize the sender, as hackers use file attachments to infect computers with viruses.