wordpress site hacked Need Help

Hi I am running wordpress blog.Now When I checked google indexed search results for my website I found that page description shows something spam like
“best site should try out for demo mode of gaming variants to adopt good gaming Participate in casino games online to take gamble online and increase your …”.Then I checked cached version of my web page and see source code it shows something spam code in header which is given below

[Hacked code removed – please don’t post that here]

Whenever I visit site from my computer I do not see above code in source of page.But google webmaster’s structured data testing tool shows that code in page html.These will affect my SEO Rankings.

I think some plugin or theme inserted malicious code in core.Please Help.