HTC Droid Incredible

So I bought this phone off eBay and it was reset to factory defaults when I got it, so I activated it yesterday and have been using it. I plugged it into my computer and started browsing folders on it. Well I found some "explicit" pictures on there. It looks like cache or temp internet files you get from browsing the web. So I am flipping out, wondering what else is on this phone. I was on the phone with Verizon for about 45 minutes, talking to 2 different techs, and they had me do a factory reset (again) which is supposed to erase everything off the phone and they're still there! They had me clear cache, browsing history, etc but they were still there!

Now I know I can just delete them through Windows Explorer when browsing the folders, but my concern was what else is on this phone that I don't know about that may creep up later? The Verizon guys were completely stumped and finally told me to just delete the files themselves, and that there "shouldn't" be anything else on there since the factory reset (although they admitted that the factory reset was not working the way it's supposed to, so they don't really know whether there is anything else on there).

Anyone experience this or know of a way to get around this? I was about to right click the folder in Windows Explorer and choose to format it, but I didn't know if that would completely erase the OS and the Verizon guy didn't know either.