What you're describing likely is unrelated to malware and is probably a hardware problem. That's the symptom I had when the video on my iMac (purchased in 2005) started going bad. It finally got so screwy that I couldn't read the screen at all, and then it went dark. Repair guys told me I'd have to replace the whole motherboard (since the video isn't a separate card on an iMac -- it's integrated into the motherboard). I decided to kiss it goodbye and buy a Mac Pro.

My recommendations would be:
1. Do a thorough backup of your system, especially the files you created. (I hope you do regular backups already, but if not, this is a good time to start!)
2. Take your machine to a repair tech, either Apple or Apple-certified, and get them to check it out.

While you're at it, it wouldn't hurt to check for the DNS Changer malware that's causing so many people's hair to catch on fire:
http://www.dns-ok.us/

More info about that here:
The Virus That Really Will Kill Your PC July 9, Discovery News

Also see:
http://www.dcwg.org/fix/
http://dns-ok.gov.au/information.html

Good luck, and keep us posted!

It's also free.

I have never had anti-virus software on my macs, but decided to install it when I got my new MacBook Pro.

http://www.sophos.com/en-us/products/free-tools/sophos-antivirus-for-mac-home-edition.aspx

I use a Macbook Pro too- so far no problems today.
But I think I will visit the link you provided, jic.

BHN

FWIW, it has found no problems to date at all.

Good luck.

Again. Much appreciation!
((((((HUG)))))))))
BHN

Or are you still seeing the weird screen behavior?