In some way a dialer has been installed on my pc. I noticed that, using internet explorer, when I tryed to access to a link, an ldr.exe application started (located in C:) trying to modify my internet connection properties. Other files (dl11.exe, hooks.dll) appeared in the same directory, and a .dat file has been created in the C:/Documents and Settings/my_account/Local Settings/Temp folder.

I executed norton antivirus and deleted all infected files, including the registry key: 

HKEY_LOCAL_MACHINE\Software\WebSiteViewer 

Nevertheless these files appear any time I restart my pc and I use Internet Explorer (only the .dat file has a different name).

Do you know a solution to this problem?