Google has explained why its social network started spamming users over the weekend: the service ran out of disk space.
Some Google+ users may have noticed repeated notifications filling their inboxes on Saturday.
One user said he received the same message 12 times, but those who had turned off notifications or not received any during the time will not have been affected.
Google's senior vice-president for social Vic Gundotra apologised for the fault.
"For about 80 minutes we ran out of disk space on the service that keeps track of notifications," he said in a post via his Google+ account. "Hence our system continued to try sending notifications. Over, and over again. Yikes."
"We didn't expect to hit these high thresholds so quickly, but we should have," he said, thanking users while reminding them the system was still a "field trial".
Google also had to stress the system was not a final release, warning business users last week not to use it yet.