A few days ago, a serious vulnerability was discovered in Adobe Flash, which would allow malicious or hijacked websites to take control of your PC. This was fixed, then more were discovered.
There's a new update today, to see if you're running the latest version of flash, go to this page
http://www.adobe.com/uk/software/flash/about/ which will tell you which version you're running, and show you the latest versions available, based on OS and browser.
Visit this link in every browser installed on your computer, Chrome, Firefox, IE etc as they can be running different versions.
Make sure you're up to date, as the vulnerabilities are severe and are being exploited right now.
Ian