Joomla website security checks

We have 3 main websites built in Joomla (on one web host). Our in-house developer has just left the business and we are looking for somebody who can close any security loopholes on the websites, e.g. Jooma platform, SQL, passwords and any other suggested entry points that you can think of.

We are looking for this to be completed ASAP for obvious reasons. Preferably someone with great Joomla knowledge as this may lead to further support work on the websites.