No. This is not true.
As near as we can tell, these slanderous statements originated from the bitter author of UltraFXP who was served a cease and desist order by IniCom, FlashFXP's publisher. They follow a trend of recent statements posted on various forums by him.
Be assured with hundreds of thousands of FlashFXP users, many of them highly skilled with computers and network security, that someone with better english skills would have come forward with hard evidence by now.
Thanks for your concern, we value your loyalty and trust.