Got a copy of Excel 2007 handy?
Try multiplying 850 by 77.1 - the answer should be 65535.
Excel 2007 thinks it's 100000.
Older versions of the spreadsheet - as well as the latest versions of the OpenOffice.org and Gnumeric packages - get it right.
The problem, replicated here at ZDNet UK, was reported a couple of days ago on the Microsoft Excel newsgroup , and looks like an elementary programming cock-up.
Excel is the mainstay numerical application of many finance houses, banks and other institutions. A basic mathematical problem like this is extremely serious, and the fact that it exists and has slipped through testing is a major embarrassment for Microsoft.
No two - or two to the power of sixteen - ways about it.
More on this as we add it up...