Severe threats typically are remotely exploitable vulnerabilities, which can lead to system compromise. Successful exploitation does not normally require any interaction and exploits are in the wild. There exists a high possibility of potential system damage or security flaw. Attacker has complete control over your computer or install new software on your machine.
Trojan.Downloader.Thun disables the Windows Firewall and changes the computer security settings to download and allow other malicious software.
Trojan - A Trojan software is any software on a user's computer that the user is not aware or intentionally installed. Most Trojan software is designed to perform some sort of actions that could jeopardize the user's security or privacy.