An ongoing multi-day outage at cloud computing services provider Rackspace has been blamed on a ransomware attack.

The service went down on 2 December due to a "service incident" and is still unavailable.

"Alongside the Rackspace Technology internal security team, the company has engaged a leading cyber defense firm to investigate. Immediately upon detecting the incident, the company took proactive measures to isolate the Hosted Exchange environment to contain the incident," the company said in a statement.

Rackspace believes that the ransomware incident was isolated to its Hosted Exchange business.

"Although Rackspace Technology is in the early stages of assessing this incident, the incident has caused and may continue to cause an interruption in its Hosted Exchange business and may result in a loss of revenue for the Hosted Exchange business, which generates approximately $30 million of annual revenue in the Apps & Cross Platform segment," the company said. "In addition, Rackspace Technology may have incremental costs associated with its response to the incident."

In its statement, Rackspace did not provide any timeline for services to return.