Dangerous Trojan is very similar to Unknown Trojan. It shows this fake message:
System Error! Your system was infected by dangerous Trojan. Note: Your critical files can be lost! Click OK to download antimalware application to clean your system! (Recommended)
and tries to scare you. It promotes Files Secure - fake-antispyware software.
It may change Yahoo and Google search engine result pages.

Files Secure 2.1 is a fake anti-spyware software. It is installed on your computer by fake codecs. It scans your systems and shows fake messages like these:
Critical System Error!
Your browser was hijacked by Trojan.Win32.Agent.akk
You need to clean your system immediately, in other case [SIC] it can be crashed soon!
Click OK to download the high-tech antispyware protection software! (Recommended)

Your computer was hijacked by Trojan.Win32.LinkReplacer
It's dangerous for your system, some files can be lost and your browser can be slow!
Click OK to download the antispyware program to clean your computer! (Recommended)
Files Secure 2.1 does not remove spyware it just shows fake messages and pushes into buying commercial version of software.
Remove this fake software immediately cause it can recreate itself.