Gregory Perry wrote to OpenBSD project chief Theo de Raadt a few days back, explaining that he was revealing this information now because he could - his non-disclosure agreement with the FBI had expired.
"I wanted to make you aware of the fact that the FBI implemented a number of backdoors and side channel key leaking mechanisms into the OCF, for the express purpose of monitoring the site to site VPN encryption system implemented by EOUSA, the parent organization (sic) to the FBI," Perry wrote.
He said that this was probably the reason why people inside the FBI were advocating the use of OpenBSD for VPNs and firewalling.
De Raadt responded to the mail on one of the project's mailing lists, saying: "It is alleged that some ex-developers (and the company they worked for) accepted US government money to put backdoors into our network stack, in particular the IPSEC stack. Around 2000-2001.
According to Wikipedia, IPsec is a suite of protocols for securing IP communications by authenticating and encrypting each packet of a communication session. There are also protocols for establishing mutual authentication between agents at the beginning of the session and negotiation of cryptographic keys to be used during the session.
"Since we had the first IPSEC stack available for free, large parts of the code are now found in many other projects/products. Over 10 years, the IPSEC code has gone through many changes and fixes, so it is unclear what the true impact of these allegations are," De Raadt wrote.
Code which is released under the BSD licence can be used freely in any system; it can be locked away in a proprietary system as well.