Telcos the world over were running networks tantamount to “technology sandwiches” where layers of legacy kit had created such high complexity that operators were unaware of glaring holes which Langlois regularly revealed in penetration tests.

via Lone packet cripples telco networks – Networks – SC Magazine Australia – Secure Business Intelligence.

“We accessed [an operator’s] systems through their x25 network which they never knew was running because the network vendor never disclosed it — it was just underlying technology.”