pagefile\hiberfil.sys virus

Does anyone know how a virus is able to infect a computer once it gets into pagefile.sys or hiberfil.sys ?
Is there a way to prevent this?
The reason for the question is once these files are infected they cannot be detected by virus\malware scans (except when the hard-drive is removed and scanned by another PC) or if detected, cannot be removed (except by deleting the pagefile\hiberfil.sys files)

 

How to Clear the Windows Paging File at Shutdown:

http://support.microsoft.com/kb/314834

I want to delete the hiberfil.sys to save some disk space:

http://answers.microsoft.com/en-us/...ome-disk/ef41dcef-ed7a-447f-82da-e04c2b4dae11

 

You don't ever need to specifically clean these files.