Users were a bit put off with a recent update to Office 2003 which resulted in many types of old files being locked out, Citing security concerns, Microsoft opted to bar users from opening old files which could put them at risk. While users have the option of disabling this "Feature" via a registry hack, for many that have archives of documents it could be a problem.
Now, Microsoft has admitted they made a mistake. The workaround they posted was too complicated, and they have stated the information they provided was in fact wrong. Rather than the files themselves being a security risk, it seems the way Office 2003 parses the documents is actually where the security risk comes into play - go figure.
Microsoft claims they posted the complicated registry workaround only because they thought only a few people would need it - so much for supporting the little guy. Either way, they claim it was a mistake - and addressed it. Now there are downloadable updates which unblock older files, without having to root around in the registry.