The Paharma Hack (or Blackhat SEO Spam Hack) is a very elaborated hack wich is often unobserved for the regular visitors - and website owners - because does an ingenious trick: present a different version of your site for the searchengine bots. The site, for a long period of time looks and behaves normally for the regular visitors. This attack is very interesting because it is not visible to the normal user and the spam (generally about Viagra, Nexium, Cialis, etc) only shows up if the user agent is from Google’s crawler (googlebot). Also, the infection is a bit tricky to remove and if not done properly will keep reappearing. It's one of nastiest hacks you might have. We recommend hiring a specialist to remove it, because generally the infection reappears in no time after the site is "cleaned".
Purpose of Hacking
It is done to redirect traffic to pharma/porn sites when visitors click on the search results in Google/Yahoo/Bing search results. Upon clicking Google sends them to the infected site and using compromised .httaccess they are then redirected to some pharma or porn site where they make little money using affiliate links.
What is the side affect?
Search engines have implemented tools to detect the compromised sites and will penalize them. They will start showing as "site compromised" to visitors. Since search engines will see modified version of pages containing pharma etc content and links - your site ranking will be geared towards those terms by Google/Bing etc. Your site will start plunging in the search for the actual products/services you may be selling. Once you lose the ranking it'll take months to recover. And if you are operating in a very competitive niche, if you don't act fast you might never fully recover.