Talk with your students about the required technology.
Ensure your students have the required technology and provide alternatives and options to those who need them. IDD Blog has some suggestions on low-immediacy and low-bandwidth ideas.
Consider making the exam “open-book”.
Unless invigilated, students will easy access to the internet and many other resources. Students should study for an open-book exam just as they would for a closed-book exam.
Use application-based and analytical questions. 
Multiple choice questions from book publishers are easily found online. Finely honed questions that ask students to apply concepts and analyze, explain, and interpret will paint a clearer picture of their learning (while being harder to find answers for on the Internet).
Request students create a quick-reference page.
Open-book exams with application-based and analytical questions can be daunting for students. Help them organize their thoughts and notes by creating a quick-reference sheet they can use to quickly find concepts and information during the exam.
Do a dry run.
Moodle gives you the ability to “Preview” a test just as a student would see it. Try to complete the test within the same timeframe and parameters as your students will have. For some students, this will be their first time completing an online test, and some may be completing it on a cell phone. Test out different variations and perhaps revisit strategy #1 with your students if required.