how do I report a player for sending me a threatening voice message?

Calling out gamertags is not allowed on the forums.Reporting on your console is the only way to report someone,there is no other way.

DDoSing should fall under the category of Bullying and Harassment.

the only problem is that unless the other player messages you that they are going to do it, there is no way to know who to report.

if they send a message then you can report that for threatening behaviour.

People with the power to ban you,xblpet,do not send threatening messages first they just do it.

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Block and report anyone that threatens you on live.

If it is in your messages report the message, report the player, block the player and if you feel threatened phone and report to the police.

How to file a complaint:

1.Press the Guide button on your controller.

2.Select Friends, then go to the Players tab.

3.Select File Complaint. Then select File Complaint again on the next screen.

Select Tampering.

Select System Tampering.

Select File Complaint.

You can also file a complaint under Text and Voice Communications and Text Message/Voice Message/In-Game Voice (depending on how he's threatened you).

How to avoid a player:

1.Press the Guide button.

2.Select Friends, then go to the Players tab. Select the player’s gamertag.

3.Select Submit Player Review.

4.Select Avoid This Player

5.Select why you want to avoid the player: Communication, Game Behavior, or Player Skill.

6.Select the specific reason why you want to avoid the player.

How to block communications (only works if messages were received from other players):

From the Xbox Dashboard, open a message from the player, and then select Block Communications. The player will not be able to send you any messages unless you send them one first.

What to do if you get IP Flooded or DDOS'ed on Xbox LIVE:

Please read this FAQ written by Microsoft Support staff here:
support.xbox.com/.../dos-attacks-faq