Is there software that I can install to remove this? How can i re-configure my system to its original settings?
What makes you believe that? No viruses currently affect OS X. Malware is scarce and it is unlikely you have come into contact with any. Before installing any commercial anti-virus software (choosing one that isn't a scam or harmful is a daunting task), tell us the symptoms.
your macbook is safe.
the best anti virus is already installed in your macbook. it's called OS X Snow Leopard or Lion that is updated.
if however, you want to make sure, download clamx av and scan your macbook with it.
why do you need to reconfigure your macbook? what did you do?
Helpful Links Regarding Flashback Trojan and Virus Protection
An excellent link to read is Tom Reed's Mac Malware Guide.
A link to a great User Tip about the trojan: Flashback Trojan User Tip.
To check for the trojan: Anti Flashback Trojan 2.0.4.
A Google search can reveal a variety of alternatives on how the remove the trojan should your computer get infected. This can get you started. Or the preferred method is to use Apple's protection tool: Flashback Malware Removal Tool 1.0.
Or, open Software Update. If you do not have the Apple protection software installed it will download and install it via Software Update. If no update appears that means you either already have it installed or it isn't needed for your system. The software is only available for Leopard, Snow Leopard, and Lion versions of OS X.
Also see Apple's article About Flashback malware.
For general anti-virus protection I only recommend using ClamXav.
For the DNS Changer malware see the following:
Will your internet service cut off on July 9?
DCWG | DNS Changer Working Group
How to remove the DNS Changer malware
If you wish to return your computer to factory settings then you need to boot from an installer disc or Recovery HD, erase your hard drive then reinstall OS X.
my yahoo account was hacked; 100s of emails were sent to my contacts and now I am getting a auto download window for a critical microsoft update...
MS Office just upgraded to Service Pack 2 for MS Office 2011 for Mac - that's not a malware problem, just the auto-update that you have turned on for MS Office. I installed the upgrade yesterday and have had no problem with my Office applications.
As to how your Yahoo account got 'hacked' - I have no idea. But it's not likely a problem on your end but rather a Yahoo problem. I would contact their customer support and let them know exactly what happened and if there's anything they can do on their end.
I wouldn't worry about any malware - just never install MacKeeper. And if you're just paranoid, you can always use ClamXav to scan your files if you like. It's free and doesn't interfere with your system in any way.
Good luck,
Clinton
Wow - good find! I'll bet that the OP will find that's his problem.
Clinton
You can install Norton AV for free (currently) from the App Store.
I think I have a virus or malware on my macbookpro
