Some applications build in security at the application level, like SSL in most Web browsers. This can protect data traffic and is usually transparent to the user. But in general, the security at the application level can be variable, and depends on the developer's implementation.

It should not be forgotten that application-level security can ward off an attack in the upper levels of the protocol stack conducted at or near the destination machine (once the datagram has passed the gateway and is being transported to the destination machine, for example). Used alone in external transit, however, the true addresses of the packets can be spoofed. Also, application-level security tends to execute slower than optimized network layer security does.