Fascinating story of a covert wiretap that was discovered because of an expired TLS certificate:

The suspected man-in-the-middle attack was identified when the administrator of jabber.ru, the largest Russian XMPP service, received a notification that one of the servers’ certificates had expired.

However, jabber.ru found no expired certificates on the server, ­ as explained in a blog post by ValdikSS, a pseudonymous anti-censorship researcher based in Russia who collaborated on the investigation.

The expired certificate was instead discovered on a single port being used by the service to establish an encrypted Transport Layer Security (TLS) connection with users. Before it had expired, it would have allowed someone to decrypt the traffic being exchanged over the service.

The major browsers natively trust a whole bunch of certificate authorities, and some of them are really sketchy:

Google’s Chrome, Apple’s Safari, nonprofit Firefox and others allow the company, TrustCor Systems, to act as what’s known as a root certificate authority, a powerful spot in the internet’s infrastructure that guarantees websites are not fake, guiding users to them seamlessly.

The company’s Panamanian registration records show that it has the identical slate of officers, agents and partners as a spyware maker identified this year as an affiliate of Arizona-based Packet Forensics, which public contracting records and company documents show has sold communication interception services to U.S. government agencies for more than a decade.

[…]

In the earlier spyware matter, researchers Joel Reardon of the University of Calgary and Serge Egelman of the University of California at Berkeley found that a Panamanian company, Measurement Systems, had been paying developers to include code in a variety of innocuous apps to record and transmit users’ phone numbers, email addresses and exact locations. They estimated that those apps were downloaded more than 60 million times, including 10 million downloads of Muslim prayer apps.

Measurement Systems’ website was registered by Vostrom Holdings, according to historic domain name records. Vostrom filed papers in 2007 to do business as Packet Forensics, according to Virginia state records. Measurement Systems was registered in Virginia by Saulino, according to another state filing.

More details by Reardon.

Cory Doctorow does a great job explaining the context and the general security issues.

EDITED TO ADD (11/10): Slashdot thread.