[mannykannot]

If I am not mistaken, there have been many cases where prior art was available (and in some cases quite well known within the field) but did not come to the attention of the examiner (or the examiner did not recognize its relevance), and the patent was granted anyway. In fact, there was one such case on the HN top page today.

https://news.ycombinator.com/item?id=31881973

Once that happens, getting it revoked is no easy task.

[hedora]

Getting it revoked is likely harder than successfully defending against a suit. Many aggressors will fold at the "here is obvious prior art, go find someone dumber to extort" phase.