Character-limited social network Twitter on Thursday announced a lower-than-expected number of monthly active users for its just-completed fourth quarter, a figure that the company blamed in part on problems in Apple's rollout of iOS 8.

Update: The issue was twofold, Costolo told BusinessInsider. 3 million active users were lost after Apple stopped auto-polling Twitter feeds for Safari's Shared Links feature, while a further 1 million were lost due to encryption changes in iOS 8 that caused trouble for some users attempting to log in.

To clarify from yesterday's call: there was no bug or issue with iOS 8. It is an issue on Twitter's side as users upgraded. — TwitterIR (@TwitterIR) February 6, 2015

During Twitter's quarterly conference call, CEO Dick Costolo said that an "unforeseen bug in the release of iOS 8 as it related to Twitter" was a drag on user growth, according to Bloomberg. "We moved on multiple fronts to minimize its impact but it wasn't a one-size-fits-all fix," he added, without going into more detail.

Twitter CFO Anthony Noto later quantified the loss, saying that the bug cost Twitter some 4 million new users. Those users could have bumped Twitter's monthly active users — a closely-watched benchmark of growth for the company — Â from the 288 million that it reported to the 292 million that Wall Street expected, though the miss was softened by strong earnings growth and a new search deal with Google.

It is unclear to which bug Costolo was referring, thought it has since apparently been fixed. "We obviously have a great relationship with Apple," Costolo said later in the call.