tl;dr: of what's going on:

A large % of the hashing power is "SPV mining" where they mine on top of headers from blocks that they haven't actually verified. They're do this because in most cases you earn more money doing it - latency matters a lot and even 1MB blocks take long enough to propagate that you lose a significant amount of money by waiting for full propagation.

However, this also means they're not checking the new BIP66 rule, and are now mining invalid blocks because of it. (another miner happened to create an invalid, non-BIP66 respecting block) If you're not using Bitcoin Core, you might be accepting transactions that won't be on the longest valid chain when all this is fixed.

Bitcoin Core (after 0.10.0) rejects these invalid blocks, but a lot of other stuff doesn't. SPV Bitcoinj wallets do no validation what-so-ever, blindly following the longest chain. blockchain.info doesn't appear to do validation as well; who knows what else?

edit: FWIW, this isn't a BIP66-specific issue: any miner producing an invalid block for any reason would have triggered this issue.

More info plz

I am using Bitcoin Core (old version, yes I am lazy and paranoid). So basically you are saying if I start my wallet now and it update blockchain it will be corrupted and I will lose access to my coins?

blockchain.info and blocktrail.com are on different chains, this may be proof we really do have a fork.