Q: I am getting a message in the middle of my imac screen instructing me to hold down the on-off button and turn off the machine. The message is in several foreign languages beside english, and there is not way to get rid of it. The curser is inactive.

That sounds like a kernel panic. These are generally hardware related, often caused by poorly seated or fauly RAM.

What is a Kernel Panic?

http://support.apple.com/kb/TS3742

and  http://support.apple.com/kb/TS1892?viewlocale=en_US

http://developer.apple.com/mac/library/technotes/tn2002/tn2063.html

More details here:

http://www.thexlab.com/faqs/kernelpanics.html

Useful articles on how to avoid and eliminate kernel panics here:

http://reviews.cnet.com/8301-13727_7-10344626-263.html?tag=mfiredir

http://www.macworld.com/article/2027201/how-to-troubleshoot-a-kernel-panic.html# tk.nl_mwhelp

As Klaus indicates, that's a kernel panic, not any kind of malware. Kernel panics are generally caused by one of three things: bad third-party kernel extensions, a badly corrupt system or bad hardware.

If you can post the contents of your latest kernel panic log, we can help point you towards a solution appropriate for your particular case. See:

http://support.apple.com/kb/HT2546