Microsoft is pulling no punches with a new promotional campaign for its revamped Outlook email service, as it directly accuses Google of "invasion of your privacy" and "going through mail to sell ads".
The campaign - which Microsoft calls "Scroogled!" - takes the form of a website that appears to have been built exclusively to criticise Google's mail services.
"Think Google respects your privacy? Think again," says the website's bold heading.
"Google goes through every Gmail that's sent or received, looking for keywords so they can target Gmail users with paid ads," it continues.
"And there's no way to opt out of this invasion of your privacy," the Scroogled site concludes.
It's the above statement in particular that could be raising alarm bells in Google's legal department. The company has long promoted transparency on its personalised advertising system, offering Gmail users a clear option to opt out of the scheme via its Ads Preferences page.
Microsoft goes on to offer a series of statistics to back up some of its claims. According to market research firm Mozaic Group, says Microsoft, 71 per cent of Gmail users are "unaware their email's words are used to display ads".
Once this was revealed, 60 per cent of Google users apparently said they would consider switching or would "definitely switch" from Gmail.
Microsoft fails to mention that it also uses scanning techniques on the emails of Hotmail/Outlook users, including domain targeting, reading the sender address of incoming mail, and picking out company names for targeted advertising within the mail client.
Microsoft and Google have a long history of smear campaigns against each other's email solutions. 2011 saw Google launch its "Email Intervention" campaign, while 2012 saw Microsoft's viral Gmail Man video appear.