I sat down at my computer this morning and could not access any web sites using Firefox. FF was telling me that "Firefox is configured to use a proxy server that is refusing connections." So I check my settings and sure enough, it's set to "Use System Proxy Settings." Thinking this was suspicious, I checked IE, and sure enough it's set up to use a proxy. But just like FF I couldn't actually browse to any sites until I set to option to "No Proxy".
Now I don't use a proxy and never have before. So I'm not sure how these settings "magically" appeared. I imagine they can be set through a registry entry. Does it seem likely that I have a virus or some sort of malware? I am running Win7 64-bit and for AV I'm using MS Security Essentials. I ran Malwarebyte's Anti-Malware but no problems were detected. Are there any known legitimate programs that will change the proxy settings without warning?