Users of instant messaging app WhatsApp should switch to an alternative, now that it is being acquired by social media giant Facebook, according to Thilo Weichert, a commissioner of Germany's data privacy watchdog ULD.
Facebook announced earlier this week that it would be acquiring WhatsApp in a deal that values the fast-growing company at $19bn (£11.4bn) - or $42 (£25) per active user.
But the takeover - the biggest ever in the technology sector - will cause a flurry of privacy issues, said Weichert.
He believes that users' privacy may be compromised as Facebook will try to extract data it gets from WhatsApp, merge it with the communication metadata it already has from its servers and attempt to monetise the combination of data.
He claimed that both Facebook and WhatsApp "refuse to comply with European and German data protection regulations", stating that both companies are based in the US where data protection laws are less strict. He said that "even the NSA access to communications data is facilitated by the purchase".
Facebook's dispute with German data protection authorities has been ongoing. The authorities want the social network to adhere to German privacy laws - something Facebook believes it doesn't have to do as it processes European data at its headquarters in Ireland. Both the German data authorities and Facebook have won appeals in their favour within the courts, but their dispute has not reached a final conclusion.
Meanwhile, WhatsApp is described by Weichert as being "very hesitant and opaque" in the past, when it has dealt with "massive security problems", such as a design flaw in its cryptographic implementation that could have allowed attackers to decrypt intercepted messages.
But in response, Facebook has insisted that it will run WhatsApp as an independent business, and continue to invest in Facebook messenger.
Despite this, Weichert suggests that users should switch to messaging app alternatives Threema or myENIGMA, both of which use end-to-end encryption.
Meanwhile, Facebook is thought not have been the only company involved in talks with WhatsApp over a possible takeover. Forbes reports that Google offered $10bn to acquire the app - but sources say the bid faltered because Google did not promise a board seat to WhatsApp's founders.
The Information claims that Google chief Larry Page met with WhatsApp CEO Jan Koum as late as last week in an attempt to disrupt negotiations the messaging firm had with Facebook. Page is reported as telling Koum that WhatsApp was "a big threat to Facebook" and even offered to better the social network's $19bn offer.