The FBI is seemingly viewing retweets of extremist propaganda on Twitter as endorsements following the arrest of a 22 year-old US citizen they were investigating.
The FBI this week arrested Queens, New York, resident Ali Saleh after his use of Twitter bolstered an investigation into his attempts to join ISIS.
Saleh had been using Twitter to formulate his plan since 2013 and in court papers seen by Gizmodo his retweeting of extremist messages were mentioned repeatedly in the legal case against him.
This is not the first time FBI has used Twitter as evidence in a legal case. Earlier this year a 17 year-old Virginia resident was arrested after regularly retweeting statements about ISIS leader Abu Bakr al-Baghdadi.
In the UK social media can also be used as evidence. The Crown Prosecution Service (CPS) states on its website that: "Communications sent via social media are capable of amounting to criminal offences".