During the development of a site, me and the team decided to develop the site with my computer as a server, with me making my localhost available from outside. I have been using several settings to try protecting the site while in development, for example by adding password to XAMPP, phpMyAdmin, but recently one of the team members said to me that when he visited the site a day ago, some content on a .php page on the site (images and text sections) has been altered.
When I took a look at the site everything was like it was before, not a single character in the source code had been altered as far as I could tell. Also, the DB is intact and nothing else has happened since.
My question now is: what can I do to assure myself that the server has not been hacked into, and what can I do to secure myself from threats of this kind in the future?