Q: i feel my macbook air has been infected with virus. I used a virus infected thumb drive almost three times. every time i connect to internet it shows multitude of ads and my mac is not working like before

Click here and run the tool.

(111983)

You don't, and never had a virus. You installed an adware Trojan that was attached to something else you installed. Run the adware removal software Niel linked to. That should do it.

You may have inadvertently installed adware. Eradicating it is simple. For an explanation or how this may have occurred, how to avoid it in the future, and for one possible solution read How to install adware.

If that does not describe your problem please post a representative screenshot of the anomaly:

Screenshots (Mac):

To take a screenshot hold ⌘ Shift 4 to create a selection crosshair. Click and hold while you drag the crosshair over the area you wish to capture and then release the mouse or trackpad. You will hear a "camera shutter" sound. This will deposit a screenshot named "Screen Shot...." followed by a date and time on your Desktop.

When you post your response, click the "camera" icon above the text field:

This will display a dialog box which enables you to choose the screenshot file (remember it's on your Desktop) and click the Insert Image button. If you are not using full screen mode you can simply drag the image into the text entry field.

⌘ Shift 4 and then pressing the space bar captures the frontmost window.

⌘ Shift 3 captures the entire screen.

Don't capture or upload any information you consider personal. To edit an existing screenshot, read How to edit a screenshot.

Drag the screenshot to the Trash after you post your reply.