If you have logged in to your Santander (Alliance & Leicester) online bank recently your account may have been compromised. One of the bank's customers noticed this when he was prompted with an unusual SSL certificate warning for www.polycache.com.
What first looked like a man-in-the-middle attack turned out to be an injection which tries to look like an ordinary web analytics URL. It goes to a script at advanced-web-analytics.com which downloads another script from polycache.com which seems to hijack
the login part of the site.
The issue has recently been discussed on
Stack Overflow and Linode Community Forums.
Update: Turns out this wasn't an attack, but a "technical error" by a 3rd party that Santander uses. Still no information on who this 3rd party is or why Santander allows 3rd parties to include scripts in their online bank login page.