Not a security breach. The private key Jaxx uses to encrypt the wallet locally can be extracted by any party with filesystem access. If an attacker has access to your Windows or MacOS filesystem, they can get at your wallet. This is a design tradeoff made by the Jaxx team to increase ease of use and enable several Jaxx features. That said, if an attacker has access to your filesystem, you will likely have a world of problems beyond securing your coins…
Jaxx is a light wallet (like your pocket wallet) and not intended for storage of significant amounts of “cash”. Store only as much as you need in Jaxx and put the rest into cold storage on a device or on paper.