Chinese hackers, according to different sources, have attacked the headquarters of Telefónica, with a ransomware-type attack, in which $ 300 in Bitcoins would be requested, for each computer, in order to rescue the stolen and encrypted information.
Telefónica would be under a computer attack at its headquarters. Apparently a group of hackers has taken control of the company's computers and would be asking for money, specifically they would be asking for the release of the devices through a payment of $ 300 in Bitcoins, for each infected computer. The attack would have its origin in China, although the information at the moment is quite confusing. This hack would not affect Telefónica customers, as reported by the company, but the company's internal teams.
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The average user should not fear anything before this massive attack, since it is focused on private companies and does not affect the average user. You just have to be careful, as always and there will be no strange links or unknown websites.
UPDATE 15.04: Vozpópuli disconnects the servers for security reasons. It does not affect the average user at the moment nor does it look like this is going to happen.

UPDATE 14.39: Vodafone, KPMG, Inditex, Capgemini, BBVA and Orange confirm that they have not been infected by the Telefónica virus, according to El Español

UPDATE 14.35: The CNI's website on cryptography and computer security verifies that the attack is due to a security hole in Windows and that the attack would be a ransomware based on WanaCry. Link here (It seems that there are many accesses and it costs him to load)
UPDATE 14.25: Vozpópuli says that Gas Natural and Iberdrola have disconnected their networks for safety reasons and would not be under attack. The CNI is talking about the attack on Telefónica being based on the vulnerabilities that Microsoft revealed on March 14.
UPDATE 14.17: Antena3 reports that Vodafone has disconnected its network to prevent a computer attack.
UPDATE 14.07/XNUMX: From Vozpópuli they point out that the attack initiated or that has its known epicenter in Telefónica, which would also affect Gas Natural and Iberdrola, would be spreading to large and small throughout the country, being the largest computer attack in the history of Spain.
UPDATE 13.51: The digital medium Vozpópuli reports that Gas Natural and Iberdrola could be affected by the computer attack and Xataka comments that BBVA and Vodafone would also be affected, although BBVA has commented in a tweet that they have not suffered any attack.
The company, after detecting the attack by the internal public address system at the request of the workers to quickly turn off the equipment, according to several sources that have provided information to eldiario.es. The workers have apparently reported that they have not only turned off the equipment, they have unplugged them from the electrical outlets, the electrical couplings have been disconnected and also the VPNs, which are the internal work networks, in addition, the workers have been asked not to remove the computer equipment from the building (those that were connected during the attack).

"Blue screens have begun to appear," some of the workers report and immediately afterwards the company began to warn by the public address system to disconnect the equipment quickly. The medium eldiario.es has had access to several photographs of the workers' screens where the usual message of ransomware attacks is seen, where the hijacking of computers is specified by hackers, warning that the files have been encrypted and they request an amount to release them. The attackers have requested $ 300 in Bitcoins, a rather ridiculous amount for the type of attack that it is. They also threaten that if they do not pay on May 15, they will increase the amount of the ransom and on May 19 they will delete the data if they do not pay.
Telefónica sources have confirmed the attack, but have reduced the severity of the attack considerably. As reported to the source we use, this attack would have affected approximately one hundred computers out of a total of approximately 40.000 computers and would not affect the services offered by the company. Telefónica says that it is simply 'a computer virus', which puts the blue screen with white letters. Some counted cases, not all, would ask for the ransom in Bitcoins.

Source: the newspaper

Why does the headline not say that the attack is on computers with MS WOS?
There is no data to verify that the origin was to a computer with MS DOS and when we published the information we did not know the origin. More information has been given later.