Trojans are malicious applications that pose themselves as legitimate software in order to trick users to install them. Once on the victim's machine, it may run any number of malicious process to steal vital information or inflict damage to other software.
Agent.bgg downloads files without users permission. The key threat of this trojan is the rootkit that is dropped. When fully installed, it will mask the rootkit with the MD5 hash of beep.sys to avoid detection.