Purging Expired Session Objects

I am looking for more information relating to the warning about purging expired session objects (sorry, I don't quite recall the exact syntax). From what I have been able to glean from the little information I've found, what's happening is that when I start a new session, if the garbage collector finds an expired session of mine and purges it (which it does with a 5%?? chance), then I get this warning. What is the best way to hide the warning? Ideally, I'd like to eliminate the cause, but I'll settle for hiding the warning. I am currently considering a cron job to purge expired session files or altering the warning level so the message disappears. Is my understanding correct? Does session_destroy delete session files reliably (sort of moot, since I don't figure that users will logout reliably). Does anyone have a novel way to deal with this? Thanks, Ben