My hosts immediately took the site off-line whilst they investigated the problem.
Sorry there wasnt time to warn anyone about this, and I support their action of doing so.
In actual fact the login box was from mepislovers -
MEPIS being a linux distro. Must admit it gave me a bit of a shock too
Problem occured due to an error or config problem at mepislovers, and the reason we were seeing it here due to a hotlinked image on their servers.
Big thank you to the guys at Vidahost who responded so quickly and found out the problem was - particulary when this was "out of hours".