Macworld has confirmed a wave of reports claiming that data stored on external FireWire drives has been lost by some users installing Mac OS X 10.3 Panther.

The new OS was released last week. Threads on Apple's Support forums first alerted Macworld UK to the problem – one thread on the topic holds in excess of 140 posts at this time.

The flaw manifests itself in the following ways: users installing Panther while having an external FireWire drive connected to their Mac have seen data loss; similarly, users with FireWire drives connected to their systems have seen data loss once they reboot Panther.

The problem does not affect all users, but when it strikes, it does seem to affect external FireWire drives (both FW 400 and FW 800) from all manufacturers.

'All brands'

A manufacturer told Macworld: "We do have some customer feedback on this issue. It appears common to all brands of external FireWire drive. It appears drives can become corrupted during a Panther install or reboot."

While Apple's manufacturing partners refrained from making comments on the record, this manufacturer's comments have been reaffirmed by other parties approached by Macworld.

A spokesman for a company central to FireWire development said: "We have had reports that people are having some issues involving losing data. However, these reports have only been coming in the last few days. We will be working with partners to identify and resolve these issues."

"If we are aware of the problem I expect this means a lot of support calls are coming in," they said.

The spokesman observed that Mac users looking to upgrade to Panther may want to hold back on installation for a week, while the problem is identified and a fix found. He added that Apple would be the most likely source for a software fix.

The problem seems to afflict FireWire devices across the board. Apple has issued no response to requests to offer short-term guidance to customers.