Suraj Gadage: +Lauren Miller First sign in to search console and check the security issues section to identify the pages/section of the website hacked. Fix the security issues and then request a review in the security issues section. Once Google checks that your site is fixed, they will remove the message and will help you get your SERP visibility back (only if it is down).Hope this helps!
Jim Munro: If you do not have a clean backup to restore from, you will need to hire a firm like sucuri.net - Sucuri — Complete Website Security, CDN, DDoS Protection to clean your site for you for about USD$200. If you do not have a clean backup, make a note to backup and store one every day from now on. If you cannot afford that amount, you have no option but to delete the current site and start again. This is not something you can fix yourself. Sucuri — Complete Website Security, CDN, DDoS Protectionsucuri.net