After Jan 27 2017, it is most important to check if you're getting clean coins. On Jan 27 someone published a list of transactions that proved the bitcoins stolen in the Bitfinex hack in august 2016 started moving.

Apparently the hacker is now trying to move small chunks of the coins to bitcoin exchanges. It is likely that they might try to use a mixing service to clean the bitcoin or that they will even set up their own mixer.

Therefore always check where did your bitcoins came from - even if you just deposited them for lending on Poloniex. You will probably not be getting back your original bitcoins but bitcoins with a different history.