I suspect that my system has been hacked into. I see huge drops in free hard disk space for a while and then the space returns to near old values. A few days ago, when I clicked "my computer", I saw the properties of the computer instead of "my computer". Start menu showed me the same thing. I rebooted my system and things became normal. All my browsers hang for a while. Additionally, sometimes my FB login page looks weird and unlike the regular page (browser injection?) Then, there are these chinese alphabets in the attached image:
Is it possible that my system is infected with some stealthy malware? If yes, how do I check if it is really malware?
I am worried to death now. All the paid av, sandboxing, no-scripting finally might have amounted to nothing. :(