The phrase "are most vulnerable when" is correct and usable in written English.
It can be used to describe a situation or condition in which someone or something is at a heightened risk or exposure to harm or danger.
Example: "Children are most vulnerable when they are left unsupervised in unfamiliar environments."
Alternatives: "are at greatest risk when" or "are least protected when".
These days they are most vulnerable when they trek out to do women's work -- fetch firewood.
Young birds (eyasses) are most vulnerable when they are fledging – taking those first not-so-graceful flights to independence from their parents.
They divided more slowly — and, since cancer cells are most vulnerable when they are dividing, that suggested that the Hodgkin's schedule needed to be a lot longer.
Ships are most vulnerable when they are refueling -- the Navy destroyer Cole was bombed by Al Qaeda while it was refueling in the port of Aden in Yemen, for example -- and guarding fuel convoys in Afghanistan has been particularly hazardous for American Marines: one dies for every 50 fuel convoys that come into Afghanistan, he said.
"Children are most vulnerable when they are old enough to be allowed to go to the mall or the movies on their own," said Parry Aftab, a lawyer and executive director of Cyberangels, a New York City-based online safety watchdog group that has consulted with Long Island police departments.
Krawcheck: Women are most vulnerable when they are ignorant.
We're hurting right now and sometimes that's when you're most vulnerable, when you're wounded".
He has tended to swoop in when a family business is most vulnerable, when it is changing shareholders or when a younger generation is taking over.
"Toyota was most vulnerable when the auto industry was booming," said Jeffrey K. Liker, a University of Michigan professor and author of a book about the Japanese carmaker.
That is pretty rare in modern politics, and means Mr Cameron has something to lose.Mr Cameron is most vulnerable when it comes to Mr Coulson.
But from the start, the initiative — begun by Mayor Richard M. Daley in 2003 — overlooked the young homeless people who can be most vulnerable when living on the streets, experts said.
