Hi, this is something i have done many times for clients. Usually arises from using nulled/old copies of website themes or plugins that contain the code, which then becomes active when installed on a live domain. I can quickly and thoroughly search your website and quarantine all the suspicious files for you. The error message will not be removed immediately, it will take some time for the bots to re-crawl your website and update the status in google. Let me know if you need my assistance, will be fixed by the end of the day. Thanks for reading my bid.
Kind regards,
Grant.