I have a website that I put online via a Web Hosting Provider. For 2 years, no problem. But recently a customer called to tell me that his computer was infected by the Downloader.Trojan virus which he got by visiting my website. When I went to my website to check it out, my antivirus program warned me that the Downloader.Trojan was being blocked from my site. (I think the trojan was associated with images on my site.) I've fixed the problem by deleting all the files from the host server and uploading the virus-free files from my computer.

So my questions are (1) how is it possible for any of the files on my website, which is hosted on someone else's server, to acquire the Downloader.Trojan virus? Is their server somehow compromised? (2) Can someone other than me alter the files on their server after I've uploaded them? And (3) how can I protect my website from acquiring a virus so this doesn't happen again?

It could be a direct infection on the server or a security issue on your web site or host server that allowed a hacker to infect your pages.

I think something similar happened to one of my sites. I changed my password after I noticed some altered code on several pages and haven't had that problem since.

I'm not a server guru, but here is what I have to say.