Hacked

Someone hacked one of my sites. They changed the homepage and that seems to be it, but it was liked that for 3 days before I noticed. I have been hacked once before. That one was a case of someone creating a folder and leaving links to some spam site in Russia. I didn't notice that for months. This one worries me more because I'm not sure how the person gained access. The previous time was due to a problem with the ftp settings that my provider had set up. This one might be a stolen password or maybe not.