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Some users have been experiencing a problem where using DAV to access their file storage would result in a large number of "logins" occuring to their account. Because of abuse tracking systems, this would possibly result in their account being locked. This problem seems to have started recently especially for Mac OS X users because of a change in the way that Mac OS X uses DAV to access file storage, it seems to use an inefficient method which sends thousands of requests in quick succession.
We've now rolled out a fix for this that will ensure that the large number of requests is aggregated into a single login event for rate and abuse tracking purposes.