From Donna’s security blog:
Claudio “Sverx” has discovered a weakness in Opera and Internet Explorer, which can be exploited by malicious people to trick users into visiting a malicious website by obfuscating URLs displayed in the status bar. The problem is that the browser fails to show the correct URL in the status bar if an image control with a “title” attribute has been enclosed in a hyperlink and uses a form to specify the destination URL. This may cause a user to follow a link to a seemingly trusted website when in fact the browser opens a malicious website.
Solution: Do not follow links from untrusted sources.