This code is added to HTML, CSS or GIF files, among others, downloaded from a website hosted by an IIS (Internet Information Services) v5.0 server that is not properly updated with the corresponding security patches. However, for image files, as those with a GIF extension, the malicious code added will not be executable.
When customers of the browser Internet Explorer visit a website hosted by an affected server, they will receive the requested site with a footnote, which contains the malicious code. If Internet Explorer is not properly updated, the malicious code will be executed without users noticing.
It is very important to highlight that the modified websites appear to be clean in the web server: it is when the request is made that the server sends the webpage with the malicious code inserted as a footnote.
If you are an IIS v5.0 server administrator, it is highly recommendable that you download the security patch available at Microsoft webpage. Click here to download the patch.
In addition, if you are an Internet Explorer customer, apply the corresponding cumulative security patch. Click here to download the patch.