I found that my Sandisk Cruzer Edge USB drive came with an autorun.inf file to run some Sandisk software. Bad, but I'll still continue using Sandisk products.
I tried to delete this and install the Panda vaccine (highly recommended), but got Access Denied problems, even using attrib -r -h -s autorun.inf in Command Prompt.
Luckily, I found this discussion: http://www.sevenforums.com/general-discussion/154065-access-denied-autorun-inf.html which said "Apparently Trend Micro antivirus blocks the access to, creation of and modification of autorun.inf files on USB drives as well." I believe this is the relevant setting.
Disabling Trend Micro Titanium Maximum Security allowed me to delete autorun.inf and vaccinate my USB drive. Although it's good to disable autorun on Trend Micro's part, the way they do this and not inform the user leads to some confusion.