Today, alot of hacker to hack your site and place his links for SEO,
This code will add his URLs when search engine bots come, cant see it when you debugging your site.(doesn’t appear to normal users, but only to Search Engine Bots)
Google allow you to debug hacked site with The Fetch as Google tool lets you see a page as Google sees it. This is particularly useful if you’re troubleshooting a page’s poor performance in search results.