The OurMine group posted messages on multiple accounts belonging to Barcelona and the International Olympic Committee.
Barcelona have accounts in several languages and relating to various aspects of the club, including their La Masia youth academy, and all appeared to have been hacked.
The hacking incident came soon after Barca beat Getafe to join Real Madrid on 52 points at the top of LaLiga.
Each account sent out the message: "Hi, we are OurMine. Well, this is the second time, the security level is better but still not the best to improve your accounts security."
The OurMine group previously hacked Barcelona's Twitter in 2017, falsely claiming the club would be signing Angel Di Maria from Paris Saint-Germain.
Barcelona acknowledged the latest cybersecurity breach after taking back control of their accounts, posting: "FC Barcelona's Twitter accounts have been hacked, which is why messages from outside our club have appeared, and which have been reported and deleted. The tweets were made through a third-party tool for data analytics.
"FC Barcelona will conduct a cybersecurity audit and will review all protocols and links with third party tools, in order to avoid such incidents and to guarantee the best service to our members and fans. We apologise for any inconvenience this situation may have caused."
The Olympic Games accounts were similarly attacked.
Messages from OurMine were posted across its official accounts, including those for the Olympics, Athlete365 and IOC Media, before being deleted.
The hacker group has previously targeted such organisations as WikiLeaks, Real Madrid, the NFL and its teams, Facebook, Instagram and the New York Times.
On a rainy night in Spain, Idowu added to his Commonwealth and world titles by earning victory with the best jump of his career.
The 31-year-old leaped a superb 17.81 metres on his fourth attempt, extending his previous personal best by eight centimetres to finish ahead of Romania’s Marian Oprea.
Idowu said afterwards: “I’ve always worked hard and by the grace of God I’ve come out a gold medallist.”
Idowu’s success was Great Britain’s second gold medal of the 2010 European Championships after Mo Farah had triumphed in the 10,000m.
London-born Idowu had also landed Olympic silver at Beijing in 2008 but injury problems later began to hamper his career and he failed to make it past the qualifying round in his home Games in 2012.
He retired from the sport the following year.
The head coach of the Olympic team fears Barcelona defender Mingueza and Real Madrid midfielder Ceballos will not make swift recoveries.
He was also critical of the officiating that allowed Egypt to enforce their physical game on the match that finished 0-0 in Sapporo.
Speaking about the injured duo, who were both forced off in the first half, De la Fuente said: "They are the greatest concern. They do not look good. Let's see if I'm wrong and they can recover.
"We are very concerned because they could be serious injuries."
Mingueza was on the receiving end of a sixth-minute heavy tackle that saw Ahmed Fotouh yellow-carded, and then came off in the 22nd minute.
Ceballos was replaced shortly before half-time after being fouled by Taher Mohamed, although it was seemingly unintentional when the Egyptian player stood on the Spain star's left ankle.
Asked about Egypt's approach, after they were shown four yellow cards, De la Fuente suggested they should have had more discouragement from such forceful tackling.
He said, quoted in Marca: "The other day we had a talk in which they explained to us how the VAR works and we hope that next time we will have better luck with the sanctions that take place in the field of play because today we have not had it.
"We had a meeting that explained the actions that could be punished with a red card. Today there were several of them and they were not punished as they told us."
Mingueza had a breakthrough season at Barcelona last term, playing 39 senior games after stepping up from the club's B team.
Ceballos has returned to Real Madrid ahead of the new LaLiga campaign after spending the past two campaigns on loan at Arsenal. He failed to score in 40 games for the Gunners last season and had just three assists.
The Ecuadorian sports ministry said Quinonez was found dead in the street on Friday.
Quinonez made history when he became the Ecuadorian athlete to win a global medal in a track event at the 2019 World Championships in Doha, and he held national records at every sprint distance.
The sports ministry tweeted: "With great sadness, we confirm the murder of our sportsman Alex Quinonez.
"We have lost a great sportsman, someone who allowed us to dream, who moved us....he was the greatest sprinter this country produced."
Spanish football club Barcelona said Quinonez had been a part of the athletics squad in their wider sporting set-up.
Ecuador president Guillermo Lasso tweeted on Saturday: "We are very sorry for the painful loss of Alex Quinonez, father, son, a great sprinter. Our sincere condolences to his loved ones. Rest in peace.
"Those who take the lives of Ecuadorians will not go unpunished. We will act forcefully."
Colombia's world and Olympic 400m silver medallist Anthony Zambrano, a training partner of Quinonez's, posted on social media: "Brother, I cannot believe it’s true.
"We do not deserve this. What awful news. It's a shame that life is such, but to die one has to be alive. You are great and I will always cherish you in my heart."
Barcelona stated: "Alex Quinonez had been an FC Barcelona athlete for three years since 2018."
The club's athletics technical director Vicente Egido said: "The whole athletics community is shocked by this news. Alex was an excellent person and very much a Barca man, and who was highly committed to competing, and enjoying competing, for Barca."
