PC World Article: Google squashes widespread AdSense malvertising attack
PC World Article: Malicious ads distributed 'on a large scale' by Zedo, Google's DoubleClick ad networks
If you are using Chrome, check your add-ons by selecting the menu icon in the upper right, then "Settings" then click on "Extensions" in the left column. If you don't have AdBlock or Adblock Plus here, then do the following:
1. Scroll to the bottom and click "Get more extensions"
2. Under "chrome web store" in the upper left you will see a search box. Enter "adblock" here and press the enter key.
3. Under the extensions section, choose either AdBlock or Adblock Plus (both are good) and click the blue "Free" button on the right.
4. A new tab will pop up when it is installed. You may close this tab or feel free to donate to these efforts. They provide a valuable service.
As I've stated before, it isn't ideal to block ads because much of the free content we view today is financed by them. However, self protection is our first priority and the methods used to sell ads, verify the ad purchaser's identity, and verify ad content are not up to the task and can't prevent malware.