Hello,
You have 'fake jQuery' infection - very often on Joomla installation. If you don't have other infections it's quite easy to clean, but it's not enough. You should update Joomla and VM to latest versions, but it's not so simple, it's in fact migration of data from current installation to the newly installed version.
But, so far, after cleaning I can upgrade your 2.5.18 version to latest 2.5.x and, what's most important, secure at the and (among others I'll apply patch released by Joomla community after the EndOfLive version 2.5.x)
Ok, let me know if you have any questions.
I'm cleaning compromised hosting accounts on daily basis, I've cleaned from fake jQuery and secured a lot of installations so I'm sure that I can help you. I'm still new here, on freelancer.com, that's why the price is quite low.
Regards,
Adam