Why is TDAmeritrade moving customer funds that were previously being held at Penson Financial, effective Fri 2/10/2012? link here: https://www.elitetrader.com/vb/showthread.php?threadid=235833
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Is Penson Financial safe...?

Whether Penson is safe or not is not for me to say, but that's not why TDA is moving customer accounts.

TDA has been intending to become an active FCM for a long time now, and this part of the process is finally becoming complete. They've been registered as an FCM with the CFTC for months, but just not been active while they made all the preparations to go live with customer accounts.

I think some of Penson's financial woes last year may have contributed to TDA speeding-up the timeline - but that's pure conjecture on my part.