"Hi, OurMine are here, we are just testing your security, HBO team please contact us to upgrade the security - ourmine.org -> Contact," read a message on both social platforms, Variety reported on Thursday.
OurMine has in the past broken into high-profile Twitter accounts including those of Netflix, Sony and Marvel.
It has also hacked into Twitter handles of Facebook CEO Mark Zuckerberg, Twitter CEO Jack Dorsey, Niantic head John Hanke and Evan Williams, the co-founder and former CEO of Twitter.
According to Variety, in addition to taking over the main accounts at HBO, the Twitter account for "Game of Thrones" was also exploited.
"HBO managed to scrub the offending tweets shortly after they were posted," the report said, adding an HBO spokesperson declined comment.
Earlier, an upcoming episode of the seventh season of popular fantasy drama TV series "GoT" was accidentally broadcast in Spain on Wednesday, four days before its original scheduled telecast.
The sixth episode of the season was reportedly available on-demand to subscribers by HBO Spain for one hour before being removed, media reports said.
Footage from the episode was posted on Reddit via YouTube, Instagram, Twitch and other streaming services, before being taken down.
In India, almost 10 days after the unreleased Episode 4 of "Game of Thrones" (GoT) Season 7 was leaked, Maharashtra Police arrested four people who were involved in the dissemination of the material regarding the HBO's marquee show.
The episode, scheduled to be aired for viewing in the US on August 6 and India on August 7, was leaked online from Star India.
On August 4, mobile comparison website 'Smartprix' spotted a direct link to the MP4 of the episode at Star India's own distribution site.
Later, people started downloading "GoT" Episode 4 and sharing the clip with friends on various social media platforms.
In a bid to contain further leaks from a group of hackers, HBO reportedly offered to pay $250,000 to the hackers who stole nearly 1.5TB data, including scripts of "Game of Thrones" (GoT) and other employee information, from the TV network.
The sixth episode of the season was reportedly available on-demand to subscribers by HBO Spain for one hour before being removed, reports independent.co.uk.
Footage from the episode was posted on Reddit via YouTube, Instagram, Twitch and other streaming services, before being taken down.
The full episode is being posted on torrent sites and is being uploaded with the file name "Game_of_Thrones_-_S07E06.flv".
This is actually not the first time this has happened as on many occasions episodes of the show have been leaked prior to the original release date.
As the quest to claim the Iron Throne nears its end with the final chapter of "Game of Thrones" opening next week, IANS lists shows that are coming to an end soon.
* "Game of Thrones": With a storyline that paints a whimsical world of dragons and White Walkers on one hand, and stays close to reality by showing how relationships cannot be trusted when it comes to ruling a kingdom, the show, with its story based on George R.R. Martin's novels, has become a global phenomenon. It started in 2011.
Unexpected twists and turns keep fans glued to "Game of Thrones", and its final season will be no different.
Actress Nathalie Emmanuel says the final chapter will bring closure to all the stories in an exciting, but heartbreaking way. Vladimir Furdik, who plays the villainous Night King, also said that season 8 will be packed with lots of surprises.
"Game of Thrones" Season 8 will premiere internationally on April 14. It will stream on Hotstar Premium along with the international premiere, and air on India TV on Star World on April 16.
* "Suits": The story started when a hotshot lawyer Harvey Specter (essayed Gabriel Macht) took a gamble by hiring a brilliant college dropout Mike Ross (Patrick J. Adams) as an associate in his law firm, and gave the audience a glimpse of the trials and tribulations of the legal world. The drama began in 2011.
The story has expanded its universe, and brought forward varied stories with myriad emotions -- be it a love story ending with a fairytale wedding and the highs and lows of corporate takeovers. It has been announced that the show will wrap up with its ninth season, comprising 10 episodes.
Actor Dule Hill says the show will go out with lots of drama, energy and some returning faces.
* "Supernatural": Credited as the longest-running sci-fi genre show, "Supernaturals" is all about the supernatural and paranormal. It follows brothers Sam (Jared Padalecki) and Dean (Jensen Ackles) Winchester as they join their family business of hunting down supernatural monsters. Created by Eric Kripke, it premiered in 2005, and has garnered a massive fan following since then.
The show, which airs in India on AXN, will conclude after 15 seasons. The last season will have 20 episodes.
* "Big Bang Theory": This show's universe originated with the story of how four nerds -- Sheldon Cooper (Jim Parsons), Leonard Hofstadter (Johnny Galecki), Howard Wolowitz (Simon Helberg) and Raj Koothrappali (Kunal Nayyar) -- react when a girl Penny (Kaley Cuoco) enters their life as a friendly neighbour.
With all the idiosyncrasies, quirky behaviour, cultural one-liners, including a lot of Indian references courtesy British-Indian actor Kunal, as well as dating fundas -- the story that highlights the personal life of scientists and geeks was loved by one and all, making it a phenomenon.
The show, which can be streamed on HOOQ in India, will wrap up its 12-season run with an hour-long finale on May 16 internationally.
* "Modern Family": The Emmy Award-winning show was an instant hit after its debut in 2009, and will be ending the golden run with its eleventh season.
Created by Steven Levitan and Chistopher Lloyd, the show navigates the life of members of Pritchett family and won hearts for showing a diverse picture of an American family with themes around a gay couple, adoption, dating, young pregnancy and ethnicity running at its core. The final season of the show, aired in India on Star World, is expected to come with "some surprises and big milestones".
* "Arrow": Stephen Amell's run as Oliver Queen will end with season eight, which will air soon. The final season based on the DC Comics series will consist of 10 episodes.
Launched in 2012, "Arrow" stars Amell as the titular superhero, whose real name is Oliver Queen. Queen returned home to Starling City five years after being presumed dead in a shipwreck, at which time he created the superhero persona of Green Arrow to fight crime in the city.
* "Criminal Minds": The police procedural crime drama television series premiered on September 22, 2005. It will be ending with Season 15. The long-running crime drama, created and produced by Jeff Davis, is about a group of FBI behavioural profilers.
* "Orange Is The New Black": The show, which premiered first on the small screen before its Netflix stint, is set to end after its seventh season. The critically acclaimed dramedy follows the life of women as prisoners and how they come to terms with it.
* "Homeland": The action-filled story of a spy, woven with the thrills of political drama, will end with its eighth season.
The story follows the life of a CIA agent Carrie Mathison (Claire Danes) and how she starts suspecting a celebrated war hero, who was once held as a prisoner by a terrorist group, and may in fact be a terrorist sleeper agent. It narrates how the agent risks everything in her duty to safeguard her country.
Shows like "Veep", "Jane the Virgin", "Elementary", "The Unbreakable Kimmy Schmidt", "Mr. Robot" and "Fuller House" will also wrap up soon.