Basically, the title of this post says it all, but here's some brief detail:
An old customer of mine recently asked me to help out with an online newsletter project. The ready-for-print newsletter had been designed in InDesign, which also gives the option of exporting to Flash (as an SWF file with an HTML wrapper). Everything appeared to work fine, except for the fact that hotlinks to websites weren't working when we tried it out. Even more puzzling when we noticed that e-mail hotlinks were fully functional.
After searching the forums (and finding numerous red herrings among possible solutions and helpful posts), it turns out it's to do with a security setting in Flash that prevents links being followed in locally stored files. As soon as I uploaded the files to my own web space, the links worked perfectly. Hope this saves someone a bit of time . . .