Need help for my site. Having too much problem with it.

Hello there, I wasn't sure if I'm in an appropriate section, if isn't please be welcome to move this. Thanks.

My situation is that. Last week, my site has occured a malware. When I was investigating my site, I saw a referrer from "mydomain.com/wp-includes/image/crystal/option.html" and guess what, It's a freaking redirect on a vi*gra shop site.

I even checked my webmail and it's surpricing that its has a lot of spam that most of the title is "Message delivery failed: Returning message to sender" about 90k message. (I've google it and seems it doesn't have a connection on the malware I've been Occured on my Wordpress site. Until now I didn't make any move on my site.

My plan is to make backups of my posts, then upload on on other site so that the medias would be considered, then I'll delete the entire site and Install wordpress again. I wonder if this would be appropriate.

Would google penalize me for this? and would the suspicious redirect would affect my seo? I still didn't make any backlinks for it. but I search my site on google, and one of my post was indexed (Other pages were included)
Please help me on how to resolve this malware on my site. Thanks

Are you using Nulled themes ?
Use the below tool to check for malwares and malicious codes
http://sitecheck.sucuri.net/

You do need to act fast and be smart though because if Google finds it they will mark your site with Warning in the results.Also use Malwarebytes and check thoroughly in your computer for viruses.