All of our stealth aircraft are vulnerable under the right conditions. The F-117 shot down over Bosnia was triangulated. The operators had a fairly good idea of where to look, used multiple systems to pinpoint the usually diminished (not invisible) radar return, and shot it down.
Not exactly. The aircraft was picked up when their bombbay doors were opened. They were within the Radar resolution cell at that point in time and gave a fair return. Once spotted by target acquisition Radars, a target tracker can lock on with relative ease. The SA-3 Goa has a fair Radar suite that used CLOS to shoot down the Blackbird.