Kelihos malware is often dropped and installed as the payload of other malware, such as trojan-downloaders. Some variants are also distributed via links to malicious websites that are circulated through the Facebook social network.
Once the malware has been installed on a system, it typically tries to contact a remote server and download its other components, including a backdoor that gives remote attackers further control over the affected system.
The backdoor also connects the system to a botnet under the attacker's control. The botnet (referred to as the Kelihos or Hlux botnet) is built on a peer-to-peer or P2P infrastructure, so commands are relayed through other similarly infected machines from the attacker's command and control server (a structure that makes this kind of botnet much harder to detect and shut down). Once included in the botnet, the affected system may be instructed to download other malware, or be used to send spam email messages to other victims. It may also be directed to perform other malicious actions, such as stealing Bitcoins.
When present on the system, the Kelihos malware is able to function as an information stealer. The malware looks for and steals login credentials from certain installed programs, such as FTP and mail clients and web browsers. It also harvests email addresses stored on the affected system.