Forum Moderators: Robert Charlton & goodroi
You say "it seems like the 950 penalty has kicked in". That's not something you need to guess about. If you do the searches that used to bring you traffic, you can check to see if your URLs are now at the end of results.
The -950 almost always (I suspect there's no "almost" about it) affects just certain searches and not others. If you do find that you have a -950 phenomenon happening, then please continue that discussion in the -950 penalty thread [webmasterworld.com], so we can keep a focused conversation. Also potentially helpful: Summary of -950 and -30 penalties [webmasterworld.com].
For your question about the the single link causing a penalty -- the answer is no, that's not the problem. A single inbound from a site not under your control will not give you a penalty.
I've hesitated to post in the -950 thread, as it's not the classic -950 penalty. Yes, it does rank on last page for some searches. But it doesn't show up on first page for any searches anymore - not even for their domain name or other very unique terms they were #1 for.
It is a site that has been indexed for a few years, but has been used as a landing page for PPC advertising and had very few backlinks. They've been getting links over last 2 months - dozens of good, fairly strong links, and maybe 200 bad links they purchased cheap.
They also have backlinks from other members of the same team that have little PPC sites that are hosted on the same server, so that may contribute, or be, the problem. But this site does not link out to any other.
I know many people say "incoming links can't hurt you". I believe that is probably true for established sites. But new sites with little link history? I see no other explanation for this site being hit than incoming links - either too many too fast, or links from partner sites that G sees as a spam network.