The servers are being hijacked by a backdoor Trojan as part of a campaign the researchers are calling 'Operation Windigo.' Once infected, victimized systems are leveraged to steal credentials, redirected web traffic to malicious sites and send as much as 35 million spam messages a day. "Windigo has been gathering strength, largely unnoticed by the security community, for more than two and a half years and currently has 10,000 servers under its control," said Pierre-Marc Bureau, security intelligence program manager at ESET, in a statement.
There are many misconceptions around Linux security, and attacks are not something only Windows users need to worry about. The main threats facing Linux systems aren't zero-day vulnerabilities or malware, but things such as Trojanized applications, PHP backdoors, and malicious login attempts over SSH.
ESET recommends webmasters and system administrators check their systems to see if they are compromised, and has published a detailed report presenting the findings and instructions on how to remove the malicious code if it is present."
Link to Original Source