Dyfuca consists of a downloader and a BHO (browser helper object). It's basically an intrusive adware/spyware that is hiddenly downloaded and installed on a computer.
F-Secure Anti-Virus detects and removes several variants of Dyfuca. However, if any of infected files are inside a CAB archive (usually located in Temporary Internet Files folder), FSAV might not be able to remove infected files from inside that archive. In this case, please delete that CAB archive manually.
You can use F-Secure Anti-Spyware or Ad-Aware to clean a computer from Dyfuca and a lot of other adware.