The Syrian Electronic Army (SEA) has hacked a series of high-profile websites, including the Independent and the Telegraph after exploiting an ad network that runs on the sites.
The online group is a state-sponsored organisation based in war-torn Syria that attacks public targets in order to gain publicity and promote its cause in the name of president Bashar Al-Assad.
The group has previously hacked the New York Times, Huffington Post and the Guardian.
The latest cyber attack was based around an ad network that runs on the various sites, which also included OK! Magazine and the National Hockey League in the US, with the network reportedly suffering a fault which the SEA exploited to gain access and spread hacking messages.
Visitors to the sites are seeing random pop-up messages accompanied by a blank screen that says "you have been hacked by the Syrian Electronic Army (SEA)".
A previous attack came in June when the Sun and Sunday Times fell victim to the group, with the Sun's website replaced for around 20 minutes with a message that said: "Stop publishing fake reports and false articles about Syria! UK government is supporting the terrorists in Syria to destroy it, stop spreading its propaganda."
The group used Twitter to boast of successful attacks in the past, and after hacking the Guardian in 2013, sent a spoof email to staff suggesting they change user names and passwords through a malicious link. Further passwords were then stolen and various Twitter accounts compromised.
This latest hack appears to have affected other news websites around the world, and differs from previous attacks as it does not target just one or two outlets.