For those who develop their own T/A trading systems in particular, but generally for anyone who creates files of any type iteratively over a period of time, the topic of revision control may be (and should be) of interest.
The attached documents detail the basic use of TortoiseSVN, free revision control software available on the Internet. While it, and other packages like it, are widely used by software developers, it can (and should) be used for any sort of files you create and develop yourself: eg. documents, formula language scripts, spreadsheets, drawings, etc. You wouldn't generally use it just to backup files you received from elsewhere, or for files that will never change (eg. photos from a digital camera, unless perhaps you retouch them), but it's excellent for keeping track of changes to files you periodically update. Any file could be stored in it though.
For people not very familiar with computer use, it's very common not to do any sort of backup at all, which of course is inviting disaster. The next step is periodically (but often too infrequently) copying their work to a single backup device, like a USB memory stick. While that's certainly better than nothing, for work under development it can still lead to problems if something is deleted or corrupted and then backed up. Once the deletion or corruption has been moved to the only backup copy, there's no getting the original back. That's where revision control software saves the day. Provided revisions are saved periodically to the database, all previous revisions are always available and can be viewed or retrieved at any time. With TortoiseSVN, saving changes to the database is very easy - a couple of clicks in Windows Explorer with a short optional comment. Of course the database must also be backed up regularly, which is also easy.
The reason I selected TortoiseSVN, which is based on a popular system called Subversion and with which I have no relationship whatsoever, is because it's free, very easy to install and use, and very easy to backup (at least in the basic scenario outlined in the document). It integrates itself with Windows Explorer and doesn't use a separate application (so it's for Windows users only). The main attached document was written for authors of novels, and includes examples based on that use, so I wrote the short addendum to explicitly cover use for T/A system developers. Mostly they're the same, but the information stored will be different.
The documents only cover basic use for this sort of application, although the software itself can also be used by teams of developers working concurrently on the same project with the database on a server and a Web interface. For that sort of use though, you'll need to read the help information. Hopefully the document is clear and simple enough for anyone to understand, but let me know if you have any trouble.