A virus definition released by McAfee for its consumer and enterprise antivirus products detects Microsoft Excel among other legit applications as a virus called W95/CTX. Other files detected by pattern 4715 as a virus included Google Toolbar Installer, Adobe Update Manager and Macromedia Flash Player. A new pattern, 4716, was released by McAfee to solve this however about 100 customers were already affected.

News:
News.com - McAfee update exterminates Excel
Inq7.net - McAfee 'bad pattern' update causes file deletion problems