If you have Adobe Reader 7 or earlier make sure you turn off the option "Display PDF in browser". Follow these three simple steps to turn it off.

1. Start Adobe Reader
2. Go to Edit > Preferences  or press Ctrl + "K"
3. Select Internet in Categories
4. Make sure that the Display PDF in browser is unchecked.

Make sure you follow these steps as soon as possible or someone could be going through your personal information online. The flaws in Adobe Reader can get information by only visiting a webpage. It could be used to gain way too much private information from your browser. Make sure you turn it off before you end up loosing a lot of personal information.