Hopefully this is a false alarm.
It seems bit.ly has made its way onto Google's list of sites that aren't safe to browse to.
Let's hope it gets fixed soon, because boy oh boy it's going to be inconvenient.
At the time of writing there is no mention of the issue on the bit.ly blog or its Twitter account.
Of course - and this may be utterly unrelated - bit.ly did suffer a user credential hack earlier this year.
Until more is known, it's possibly best to avoid links used by the URL-shortening service right now. Fingers crossed that there hasn't been a security breach at bit.ly, and Google has goofed up.
It appears the issue has now been resolved.
Bitlinks are no longer blocked by Google Safebrowsing in Chrome/Firefox. All services are in order. No data/Bitlinks have been compromised.
— Bitly (@Bitly) October 25, 2014