Well I don't know if I'd say cyber sex isn't cheating...
May not technically be sex, but neither would be say both people being in the same room and masterbating while watching one another. Or having phone sex....
If folks are doing that, particularly behind the back of their spouses, they are definately engaging in some behavior that I would not classify as trustworthy or healthy in terms of a long term relationship.
Either way I don't think I'd view that in the same light as flirting.
I did some teen youth leading some years ago. They had no idea what "dating" was. When I explained it to them, they thought dating was a marvelous idea, and why hadn't anyone ever thought of it. ???
Nah, I didn't feel old, from their comments, it just made me want to make things even clearer and better for the upcoming generations.