Wow. It's called years of QE causing a bubble in equities. Several years ago our Fed stopped looking at the economy as something that drove the market, and started looking at the market as something that could drive the economy. That's why the stock market has had 6 great years even as the main street economy has not. Ultimately, that's a very unstable position. This is the unraveling of that.
Throw in all the other reasons that our economy is struggling..Obama Care, EPA, taxes, regulations, etc....and it's ugly scenario.
If the Fed was purchasing stocks that would show up in SEC filings. I've never seen any report of the Fed purchasing stocks and as recently as 2012 they had never purchased stocks. That would be major news because it would give the Fed an ownership position and voting rights in corporations. The cries of conflict of interest would be loud and valid.
Fed holdings did dramatically change in 2008 but it was still all debt securities. A huge amount of mortgage backed securities was added to their mix. You can find a useful description here The Evolving State of the Fed’s Security Holdings
Any impact on the stock market is a secondary effect of the extremely low interest rates that QE produces. But we have had very low interest rates since the very beginning of Dubya's term in office. That 'war on savers' isn't new and it's been bipartisan.