Is this a bug in WORD

WORD in Office 2000 is in use for sometime now. Very recently, whilst typing a document, a string automatically appeared in the point where I was in the document. The string read the following:
VIRUS! DANGER! HARD-DRIVE UPLOAD BEGINNING!

Subsequent investigation revealed that whenever the word ‘detail’ is typed, it automatically replaced with the above string. So, now I am unable to use the word ‘detail’.

Is this a bug? how do I remove this? Any help on this is much appreciated.

Thanks.