The general gist of the message is that this attack will be in retaliation for war crimes committed by the USA against Iraq, Afghanistan, and Pakistan.
The attack is supposedly to “wipe the US government off the cyber map” and is being organized from a nation (according to Wikipedia) known for lots of not-so-good stuff:

## From Wikipedia ##
The government of Mauritania was overthrown on 6 August 2008, in a military coup d’etat led by General Mohamed Ould Abdel Aziz. On 16 April 2009, General Aziz resigned from the military to run for president in the 19 July elections, which he won. In Mauritania about 20% of the population live on less than US$1.25 per day. Slavery in Mauritania has been called a major human rights issue as well as female genital mutilation, child labor, and human trafficking.
##

According to the FBI, Open Source reporting claims that their previous attempt to “wipe Israel off the cyber map” was a total failure, with little to no impact.