whaleThird-party Twitter applications struggled to keep up as attacks on the microblogging network grew more aggressive for a second day. The company’s defensive measures put a damper on users who tweet via third-party apps and SMS text messaging.

Twitter’s Ryan Sarver, who is the product manager for the platform team, said at about 3 a.m. Pacific Time that the attacks intensified to almost 10 times what they were yesterday.

“In order for us to defend from the attack we have had to put a number of services in place and we know that some of you have gotten caught in the crossfire,” he wrote. “Please know we are as frustrated as you are and wish there was more we could have communicated along the way.”

One Twitter client, HootSuite, said they were only partly active today with Twitter under fire. The company was unable to communicate with the application programming interface (API) for much of yesterday, according to spokesperson Grace Carter.

“While we await the recovery of the Twitter API, we’ve been doing what we can on our side,” she said. “We’ve been in touch with Twitter, who have been responsive, and have assured us that they’re working on whitelisting our IPs.”

Another Twitter client, Seesmic, pushed back its updates because the service was “still too unstable.” Brizzly, a Twitter client built by engineers from Google’s Reader team, had to slow sign-ups for its private beta test.

Twitter’s co-founder Biz Stone said the company was working to restore access to the Twitter platform. “There was some overcompensation on our part as we tune our system to deal with this scale of attack,” he said.