What is this copy right infringement e- mail I got ? ?

Do NOT reply to this. you have given no information on the email address it came from, and you would need to show the full headers of this email to an authority abuse department to ensure it is genuine. it is possibly a scam to get you to give away personal information. This is a warning about posting the file, not downloading it. Unless somebody else on your connection has done this, it either has not happened, or if you have a wireless connection, it is not secured and somebody has used it to post such a file. If this is the case you should NEVER use unencrypted wireless. Contact the abuse department of your ISP, ask them to check this out.