Moved this to Malware Discussion > Corporate User Assistance for (hopefully) better handling.
Hi, thx for your help.
Yes, it has been one of the first things we did but nothing has been found.
Anyway, it seems to be fixed after a windows system restoring.
Thx for your suggestion.
That's good. After a successful restore to rid you of malware, it's best to temporarily disable System Restore which will rid your machine of the infected files.
There are lots more hints and tools in the last link in my signature below.
After a restore it is wise to ensure that all updates are installed, so I would check now.