How do I get rid of a virus?

Does the computer shutdown with no warning?

Do you get a kernal panic (screen comes down and says to reboot?)

Does the machine just freeze?

Unlikely a Virus

Does the problem persist while in safe boot Hold down shift key while booting untill apple logo appears with a progress bar)?

If you are seeing messages in multiple languages saying that you have to restart, you are experiencing kernel panics. Kernel panics are typically caused by bad third-party kernel extensions, a badly corrupt system or bad hardware. No Mac malware should cause kernel panics, but ironically, it could be a kernel extension installed by your anti-virus software that is causing the problem. What anti-virus software is it? Try uninstalling it. (If the thought of removing it scares you, read my Mac Malware Guide.)

It could be some other third-party kernel extension, as well. Copy the following command:

kextstat | grep -v com.apple

Then open the Terminal (found in the Utilities folder in the Applications folder) and paste that command in there, then hit return. Copy the output and paste it into a message here.

Launch the Console application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad. Click Utilities, then Console in the page that opens.

Select the most recent panic log under System Diagnostic Reports. Post the contents — the text, please, not a screenshot. In the interest of privacy, I suggest you edit out the “Anonymous UUID,” a long string of letters, numbers, and dashes in the header and body of the report, if it’s present (it may not be.) Please don't post shutdownStall, spin, or hang reports.

First, get rid of the worthless "anti-virus" software. It will only make matters worse.

You were given a suggestion to boot in safe mode. Did you do it, and did the problem manifest itself in safe mode?

Get rid of Avast. It has been implicated in problems on other users' systems and has a history of false positives where it identifies legitimate parts of the system as malware. It may be good on Windows, but not on a Mac.

Also, that Soundflower kernel extension has been in many kernel panic logs that I have seen here. I would recommend removing it.

VirtualBox should be okay, but make sure it's up-to-date (I don't know what the current version is), and if removing the other two programs doesn't help, try removing it as well. (That should not affect your virtual machines... you should be able to reinstall it later and pick up where you left off with the virtual machines.)

Be sure to use the uninstaller provided by the software, rather than just dragging the app to the trash.

Look in /System/Library/Extensions. Is there a file called Soundflower.kext in there? If so, move it to the trash and restart the computer.

Choose Go To Folder from the Finder's Go menu and paste in "/System/Library/Extensions".

While i Agree totally with all the info Thomas has provided (Read the Mac Malware Guide, Great article BTW Thomas), I am curious to Know whether or not you have tried booting in safe Boot yet, and whether or not the problem persists or not, reason being is that Safe boot loads only the required Kernel extentions, in which case if it is a third party kext that is causing the issue then it is likely the problem will not mannifest whilst in Safe Boot, in which case you could then start trobleshooting the Kext's (among other things), and If the problem persists (in Safe Boot) you know that it is unlikely that a third party Kext is the cause of the issue.

Also Are you getting a Kernel Pannic (grey screen with dirrerent languages telling you to restart your machine)?

or is the machine Just shutting down by itself without any Warning? (in which case it is quite possible you may have a hardware Problem)