Hi,
you are receiving BGP prefixes with private AS numbers included within the AS-PATH from your ISP?
This should not happen within the Internet, you should ask your ISP to investigate.
As a workaround, you could create some neighbor filter-list denying any private AS within the AS-PATH.
See http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_bgp3.html#wp1037204
HTH,
Milan