How credible are the rumors that the NSA has compromised IPSec?

Part of the Snowden revelations was that the NSA had targeted IPSec.

But I’m having trouble separating FUD from legitimate issues.

How credible is this? Are there ways to use IPSec to be confident against it being broken?

I like IPSec because it’s fast and standard, so I’d like to continue using it instead of say, OpenVPN if possible.