WordPress & Drupal sites are prime targets for hackers. These hackers don't want to bring you down because they dislike you, in fact most of these hacks originate from bots crawling the web, looking for WordPress and Drupal sites that are vulnerable. If the bots identify your site as a WordPress or Drupal site, they will then set up shop and start looking for vulnerabilities.
Unfortunately, most people don't take this topic seriously until after their site or sites have been hacked. It is only then that they realize that they may lose days of work just trying to regain control over their sites. More importantly, if Google identifies your site as being compromised, they will down grade your site in the search results