Win32/SillyBHO.BF is a Trojan that registers itself as a Browser Helper Object (BHO) and installs other malicious or unwanted files on the system.

Win32/SillyBHO.BF is a DLL file that is usually dropped by other malware into the %System% folder with a random filename, or with the filename "helper.dll."

When executed, it registers itself as a Browser Helper Object (BHO) by creating the registry entries.

More information can be found at this Computer Associates page.