If you've made no changes then presumably it's a server configuration change or update that's responsible? I'm curious to know why you're asking here in the forum when really the only way to be helpful with this is to have FTP access to your
website hosting and I presume you're focusing on a response from eUKhost support, so why not email them direct and a ticket will be opened?
I can confirm that I cannot see the validation image that security.php is supposed to display — I'm currently using Firefox 3 as a browser (and I also checked with IE7) — missing images in both.
Hopefully Support will fix it ...