During the last few weeks, an annoying problem has started up whenever I've had to download a file sent to me as an attachment in Outlook email. The original filename is changed by adding a prefix "UTF-8" to each name. This occurs over various different file formats, including Word documents, ExCel files and PDF files, although I haven't confirmed it for all file types as I mostly work with these three.

Can anyone explain this? More importantly, can anyone suggest a fix? If it continues, I will have to change browser...