Issue: Google has flagged your site with a "This site may be hacked" warning message.

There could be times when Google search displays a warning message under your site results that the site may be hacked. This happens when Google believes that a hacker may have changed some of the existing pages or added new spam pages to the website.

Now, if you are running a Convert experience on your site the Convert script is bound to make your desired A/B test changes to the webpage, right? But, Google may take even these into account and flag your site with a warning. However, this doesn't affect the SEO of your website, so be rest assured.

There are multiple security checks like malware scans, keeping CMS updated, etc that you must perform always to keep your website safe. However, in this case, you could also review the changes done to the site and ensure the source by following their instructions as given in the article below, this would also help you remove the warning message from the site:
Remove this message from your site