Royal Mail has confirmed that the disruption experienced on its postal services is due to a cyber attack. The confirmation was made by the CEO of the U.K. postal giant, Simon Thompson, during a session where he was questioned by the U.K. parliamentary committee.

Reports has it last week that the Royal Mail had experienced a cyber attack, which has left more than half a million letters and parcels stuck in limbo. The Telegraph reported that the attack is suspected to have been carried out by a Russian-linked ransomware gang called Lockbit.

A Lockbit representative has initially denied involvement, and pointed blames to other hackers using Lockbit’s leaked ransomware builder software. It is uncertain whether Lockbit is actually involved in the cyber attack as the cyber group has not listed Royal Mail on its dark web leak site.

The CEO, however, refused to give out specifics of the cyber attack, claiming that discussing details of the incident would be detrimental to the investigations in progress. Thompson said that the postal service continues to experience disruption to its international export services following the cyber attack.

“For export parcels and letters through our postal services, we are no longer able to provide that service. […] The team have been working on workarounds so that we can get the service up and running again,” Thompson said, adding that the Royal Mail will have “more news to share” soon.

Mr Thompson also told U.K. lawmakers that the company believes that no user data was compromised in the attack. He also told lawmakers that the organization is prepared for that situation to change, noting that the company has already notified the U.K. data protection regulator, the Information Commissioner’s Office, as a precaution.

According to David MacDonald, who spoke with the BBC, many firms have complained about how the disruption of services have affected their businesses, especially as it affects international shipping. Mr MacDonald, who runs Blue Sky Vinyl, said that about 45% of his company’s business comes from countries like Australia, New Zealand, Singapore, Japan, China, and Ukraine, and he has had to explain to customers why there is a delay in business.

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Another business owner said his company sells on platforms like Etsy, and since packages can’t be retrieved after posting, it is just sitting ducks somewhere. The business owner said the result of this is the series of low stars its company is receiving as reviews on their online platforms.

In response to packages sitting ducks in Royal Mail’s facilities, the company has asked customers to stop sending international shipments till the situation is resolved.

“To support faster recovery when our service is restored and to prevent a build-up of export items in our network, we’re asking customers not to post international items until further notice,” the company said in a statement.

Prior to the cyber attack, Royal Mail has been struck with issues since December, when postal workers staged a walkout after a longstanding dispute over jobs, pay, pensions and conditions.