i received the following info from my webhost but I've no idea how to go about this! Can anyone help!
It is likely your website has been 'hacked', most probably as the result of a weak FTP password. I would recommend republishing your entire site, over-writing all page with a clean copy; this should then erase the code which has been injected into your pages. Please make sure to upgrade your applications to the newest versions.
In addition, you should immediately change your password through the control panel for the account. You should choose a 'strong' password, which includes upper- and lower-case letters, numbers and special characters such as hyphens, and is at least eight characters long. Our suggestion when you change your password that you use a Strong Password Generator (I suggested using this website: http://strongpasswordgenerator.com/) This will help reduce the chance of this happening again.
Unfortunately our technical support can offer very limited support or insight as to how a site is getting hacked. One company we do endorse that specializes in website security is SiteLock (http://www.sitelock.com).