Are online exam proctoring services efficient and trustworthy?
According to an article of the German news site "Spiegel online": NO

http://www.spiegel.de/lebenundlernen/uni/iubh-fuehrt-on-demand-online-klausuren-ein-so-einfach-war-schummeln-noch-nie-a-1129916.html

A short summary of the article in English:
There was a test exam that was supervised externally using the students smart phone and computer. The student used his own computer where he had to install a special software. After some technical trouble, the connection to the proctor had been established. The student had to identify showing his passport, he had to present the room to the proctor via his mobile phone camera. He ensured that there are no illegal tools (additional books etc.) or other persons in the room. The mobile phone was then set up to show the student as well as his computer and keyboard. The tool on the computer enabled access of the proctor to everything that is shown. Then the test started and the proctor appeared to continuously observe him.

However, the student tried cheating and was VERY successful by doing so.
The student was able to read from an undetected cheat-sheet that was pinned to the wall in some distance. The student managed to open some book and to read in his notes, despite this was not allowed. Finally he even stood up and walked around in the room. The proctor did not react. All this cheating remained undetected.

The proctoring service has some statistics that mentions 4000 detected cheating attempts in more than 63000 online exams. The article finally raises the question how many more undetected ones took place.

From my personal experience in IT security: A computer system (and especially a room) that is under the student control should never be used for such an exam since its security cannot be guaranteed. Clone the monitor signal, have a special kernel driver in place, have the exam running in a virtual machine, ..., there are many ideas. Some might work, some won't. It is a similarly difficult task as preventing cheating in online games: A lot of effort goes in but you NEVER get rid of cheaters. As long as there is some motivation (there definitively is for university exams!), you will find people helping you cheat.