Background Intelligent Transfer Service (BITS) is a component of modern Microsoft Windows operating systems that facilitates prioritized, throttled, and asynchronous transfer of files between machines using idle network bandwidth.
The web page ends with a list of third-party applications that use BITS. However, as any technical method, it can be used for evil purposes as well. Eric Landuyt analyzed a malware that exploits it for bad:
I liked the “proof of concept” WinDbg script that runs the malware in a controlled manner. Breakpoints with actions are very powerful, indeed.
Nice work, Eric!