The Merchant Customer Exchange is informing individuals and businesses involved in the testing the venture's CurrentC mobile payment system that "unauthorized third parties" have obtained some of their email addresses.
MCX is warning those participants to avoid opening e-mails that seek financial information, or appear to be coming from MCX and asking for personal information, according to a copy of the MCX letter posted online by Business Insider.
MCX is continuing to investigate the email hack, but noted that only email addresses were obtained and no other information, according to the letter.
The security issue comes at a time when MCX is under sharper media scrutiny after some of its retailer participants stopped accepting rival mobile wallets following Apple Pay's launch. MCX merchants must work exclusively with MCX, though they can drop support for MCX without penalty, MCX says in a blog post.