Although I don’t want to sound critical of the question or appear condescending to the anonymous person who asked it (because I think it is indeed a very good question) it is still nonetheless a perfect illustration of, as one priest put it, “the narcissism of small differences” and usually arises when people lose sight of Orthodox Christianity as a whole, while getting bogged down by minutia and that which is perceived as minor to the Theology and Doctrine of our Faith.
This is exactly what happened to the Pharisees during New Testament times: they went from being a truly prayerful, pious branch of Judaism, to a sect of superior-minded legalistic rhetoricians which endlessly debated every single word and action in Scripture – even to the tithing of herbs from people’s gardens! Their prevailing mindset then caused a type of “we’re right and you’re wrong” attitude which proved divisive, misleading the Jews and guiding them further away from God’s whole.
This particular question regarding the ending of the Lord’s Prayer, however, basically comes about when we try and pit a translation against itself. The Lord’s Prayer, as it has been handed down to us from the original Greek states, “apo tou ponirou,” which can be translated as either “from the evil one” or “from evil.” Therefore, both ways of ending the Lord’s Prayer would be deemed appropriate. They obviously each convey the same essential meaning, and in my opinion, neither one should be termed more correct or “proper” than the other (although I have heard many people making cases for both). In the end, it’s not wrong to pray it either way – just make sure you pray it often and with great fervor!