[CentOS] probes on udp port 500

Last couple of days some of my hosts were probed for UDP port 500 (IKE daemon, used by IPSec for key exchange) from dialup IPs. Don't remember seeing similar probes before. Some new vaulnerability that script kiddies (and pro crackers) are trying out, or is this some old stuff? I do remember there were some security problems with racoon in the past (that were fixed in current CentOS ipsec-tools packages), but don't remember reading anywhere there were any automated tools to exploit it floating around. Or are there some new flaws discovered recently in some IKE implementations?

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