President Bashar al-Assad's government has been accused before of cutting Internet and telephone connnections to block opposition activists and rebel communications during the 20-month revolt.
Authorities had attributed the latest outage to a "terrorist" attack or a technical fault.
Anonymous have said they will shut down the Syrian governments websites around the world in response to Syria’s internet blackout. For the second day all internet services, mobile phones and many fixed line phones are out of action.
A tweet on Friday from the group read, “Government of Syria cuts country’s internet access – anonymous goes on warpath.”
Anonymous quickly called their campaign Opsyria. At 02:00 am GMT on Friday they started removing all the Syrian government’s internet properties that remained online, after the country’s Web access was severed, they also targeted domains ran by pro-government sympathizers.
Some of the Syrian organizations and companies that have been hacked by Anonymous include Syrian Railways, the Syrian parliament, Syrian TV and the Syrian Embassy in China.
The hackers also managed to download 1GB of confidential memos and emails from the Syrian Ministry of Foreign Affairs including details about plane loads of cash from Russia and arms from Ukraine, which they have uploaded for public viewing.
Syria's Internet shut down on Thursday, a move which activists blamed on authorities but which authorities variously attributed to a "terrorist" attack or a technical fault.
Global hacking network Anonymous accused Syria's government of blocking communications to silence critics and said it would respond by attacking Syrian government websites around the world.
"As we discovered in Egypt, where the dictator (Hosni) Mubarak did something similar - this is not damage that can be easily or quickly repaired," Anonymous said, referring to an Internet outage during the 2011 uprising in Egypt.
Voice of Russia, RT, Reuters