Remove $header$execute from vbulletin forum
You might see some irrelevant content on your home page of forum (most probably in the very top of site). If you are seeing such content then it might be that someone is trying to do some malicious activity on your website.
Why external code is being added to vbulletin forum
In order to insert some malicious code to forum hackers try to create various login with some special privileged there and through those privileges they manage to write malicious code into the template file of the forum. $header$execute is again same kind of attempt made on forum.
How to Remove $header$execute from vbulletin forum
>> Login to admincp of vbulletin forum
>> go to under ‘Styles & Templates’, select ‘Style Manager’
>> Under default style is, in the drop down menu select Edit Templates.
>> Scroll to ForumHome Templates and expand it. Double click on it to open it in editable mode
>> Search here $header$execute and remove that and click on save button your template will get saved.