A free add-on to Internet Explorer alerts you if you contact a server whose security has been compromised by a Linux bug that went undetected for months.

The bug in a Debian distribution generated easily-cracked Secure Socket Layer (SSL) certificates used to authenticate links used for sending sensitive data such as passwords and PIN numbers.

Some estimated that the number of machines affected run into millions – and many of them are still operating, unpatched.

The SSL Guardian tool from Heise Security watches sites you visit and warns you of the risk before sensitive data is sent over the web. You still have the option of continuing the link but the company warns: " You should assume that everything can be read by a third party."

Heise also says that the company sees nothing of your personal data. The tool protects IE, Outlook and Windows Mail; Firefox has its own tool for doing the same thing.