Serious issues with Outlook 2003 and 2007

Following receiving an email message which contained question marks and some international (Asian) characters, everytime we reply to ANY message our message gets garbled with question marks as well. Did a Google and some users (especiacially Mac users with Outlook) have had this problem but nowhere have I found any fix. We found a thread that suggested removing Word as the editor, changing message properties to plain text etc but none of those solutions made any difference. We've checked the language settings for Outlook and IE and they are set to default and we even tried adding more languages to the Office Language settings with no effect. Talking around the traps it seems that quite a few people are suddenly getting this issue over the last few weeks (we don't know who they are, so they haven't got the issue from any emails we've sent).

We've run some malware scans but nothing is found.

Can someone help us with this issue? Is there a link to Microsoft Office support where we can get help? Currrently we get around the problem by not replying to any message, but starting a new message everytime, which is a pain. We are also concerned that we may be inadvertantly spreading the problem. Also, from the Google search we did, it seems that this has also occurred with Outlook Express.

Can someone please help?