Crack in carbon fiber frame

I went to my LBS this morning to pick my bike up from being repared (bar tape, wheels trued, front derailleur adjustment). The work was done however the mechanic pointed out that the bike has a hairline crack about 2 inches long running down the seat tube. Basically the crack runs up and down the tube not around it. This crack was definitely there however I don't know if this has been there for 2 days, 2 months or what. My question is how risky is this? Am I someday looking at my bike having a catastrophic failure while I'm riding, can I keep an eye on this or should this bike go out to the curb minus the Ultegra components?