There is a rule against shorting stocks less than $5. It has to do with margin rules which, I think, say you cannot buy a stock for less than $5 on margin. And, you have to have a margin account to short stocks.
BIDU was shortable from day one. You just had to find a owner of the shares that was willing to lend them to you for you to sell them "short".
I find it quite amusing that 99% of the people on ET do not know what a "short" really is, LOL.
SteveD