Twitter couldn't tweet that it was under attack today. Twitter is the target of a denial of service attack.
Attacks such as this are malicious efforts orchestrated to disrupt and
make unavailable services such as online banks, credit card payment
gateways, and in this case, Twitter for intended customers or users. Twitter is defending against this attack now and will continue to do so.
Twitter did manager to recover and get the service working. At 9:46 am, they noted that "as we recover, users will experience some longer load times and
slowness. This includes timeouts to API clients. "