Hacked site has link to viagra in header

I’ve got a link to a Viagra vendor in my site’s header.

I only have one plugin installed: Sucuri Security.

The header.php says this:

<hgroup>
         <div class="site-logo">
           <h1 class="site-title">
             <?php bloginfo( 'name' ); ?>
           </h1>
           <h2 class="site-description"><?php bloginfo( 'description' ); ?></h2>
         </div>
       </hgroup>

The view source on the website has this:

<hgroup>
         <div class="site-logo">
           <h1 class="site-title">
             Joe Bloggs Consulting           </h1>
           <h2 class="site-description">B.Sc. Hon., FIQ, Pr.Sci.Nat.</h2>
          <a href="https://complete-prick.com/acquisto-viagra-in-linea/">Cheap Viagra</a>
 </div>
       </hgroup>

I’ve read the links published herein but have yet to find the location of the code that inserts the link.

It isn’t in the database and I’ve reinstalled the site and it still persists.

Obviously this is doing wonders for my client’s business.

??