All Internet Browsers need to be updated because of a security breach in one of the companies that issues security certificates.

The updates for all browsers will invalidate the security certificates and protect you from web sites using these fake security certificates. One of these fake security certificates pretends to be Google, so it is vital you update your browser now.

Internet Explorer (Gold Shield appears at bottom of your screen)
Mozilla Firefox (software will ask you to update)
Google Chrome (automatically updated)
Apple Safari (software will ask you to update)
Opera (software will ask you to update)

You can read more about the problem here