ref.dat is a dangerous file, which is related to several different viruses. It may be installed and used by Smitfraud, SpywareQuake, VirusBurst, Zlob.Fam and other cyber threats that pose a serious harm to computer's state and people's privacy. In most of the cases, these threats are used to steal people's money by making them purchase their fake licensed versions. For that they display fake system scanners and then show exaggerated scan results that are always filled with reports about invented viruses. Please, do NOT purchase any license that belongs to Smitfraud, SpywareQuake, VirusBurst or similar 'anti-spyware'. You should ignore their alerts and remove these programs from the system.
As soon as Smitfraud, SpywareQuake, VirusBurst or other threat manages to infect a target PC system, it creates ref.dat file. Once executed, this file acts depending on what commands are given to it. Harmless pests may use ref.dat to degrade system's performance by displaying commercial advertisements, causing redirects or performing other annoying actions. Really dangerous parasites may use this file to damage system, infect it with specific files, hijack installed software and violate victim's privacy.
If you noticed ref.dat running in your system's background, you should scan it with RegCure Pro. Please note that sometimes the appearance of this file may not mean that your PC is infected. That's why it's worth examining this file before deleting it.