The Federal Bureau of Investigations has issued a warning about a malicious software that hackers are using to infiltrate and attack businesses in the U.S. The five-page confidential warning that the FBI issued to companies did not disclose the victims of the attack but it detailed the nature of the malware and what to do should it be detected it in their systems, including contacting the agency. 

"The overwriting of the data files will make it extremely difficult and costly, if not impossible, to recover the data using standard forensic methods," said the warning, as quoted by Reuters. 

According to the news agency, experts who reviewed the FBI's report deem that the malware the agency is referring to is the same one that was used to attack Sony Pictures Entertainment's computer network. The company's computer system was breached last week, paralyzing their email and other services for several days. Reuters pointed out that the infiltration in Sony's network is the first major cyber-attack done on a business in the U.S. 

The hackers have yet to be identified. However, experts say that the malware used against Sony is similar to the ones used to attack businesses in the Middle East and Asia, including one that took down about 30,000 computers in oil producer Saudi Aramco's computer network. Wall Street Journal also mentioned that it's akin to the one used against South Korean television stations last year.  There are speculations that the hackers are working on behalf of the North Korean and Iranian governments. 

Further, there are theories that it's a move against Sony's upcoming comedy "The Interview," which features an assassination attempt on North Korean leader Kim Jong-un. 

U.N. Ambassador Ja Song Nam wrote to the United Nations about the movie back in June, saying, "To allow the production and distribution of such a film on the assassination of an incumbent head of a sovereign state should be regarded as the most undisguised sponsoring of terrorism as well as an act of war."