IRS-authorized tax service eFile.com appears to have been hijacked and used to distribute malware, researchers have found.
The website hosts an e-file software solution, authorized by the Internal Revenue Service (IRS), that offers tax returns filing services.
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The payload is a Windows botnet written in PHP. There are different versions, depending if the visitors are using Chrome, or Firefox. Most antivirus programs are now flagging the botnet as a trojan, and the website stopped serving them as of April 1. Its key functionality is giving the attackers full access to the target endpoint, which they can later use for further attacks, as well as lateral movement across the target network. Further attacks could see them deploy malware, infostealers, or even ransomware.
While the researchers did not yet determine exactly who was behind the attack, it was found that the two versions try to establish a connection to an IP address based in Tokyo, apparently hosted with Alibaba. The same IP address was also found hosting a different illicit domain.
It’s difficult to assess how many people got compromised as a result of this campaign. The full scope of the incident remains to be seen.
The news is particularly concerning as it is currently tax filing season in the United States, where consumers and businesses have until April 18 to file their tax returns. It is an event that cybercriminals often use as a starting point for their activities. Sometimes, they’d assume other people’s identities and file taxes on their behalf, in order to steal the money. In other scenarios, they’d impersonate the IRS and try to send out malware via email.
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