As the recession bites, more and more of us are turning to personal finance management tools to keep control of dwindling funds.

One of the big boy in the US is Intuit with its Quicken Online offering but it seems to have been spooked by young whippersnapper Mint, sending a nasty letter to its rival demanding evidence to back up published user figures.

Intuit is incredulous about Mint's claims that it's attracting 3000 new users a day and now has over 850,000 people signed up.

The letter, obtained by TechCrunch, says "we do not wish to suggest that Mint.com is engaging in false advertising", but the claimed jump in user numbers is "of some concern".

Mint CEO Aaron Patzer told TechCrunch the site actualy has 934,000 registered users, of which a pretty impressive 680,000 have linked to at least one bank account.

Obviously Intuit doesn't come out of this too well, appearing to be more than a little worried, even paranoid, about the competition. The firm told TechCrunch it's common business practice to send these kinds of letters but that doesn't make it look any less ridiculous.

And this isn't the first time Intuit has demonstrated a thin skin. Last month the firm felt the need to rush out a statement defending its TurboTax software after Treasury secretary nominee Tim Geithner revealed he had used it to complete his incorrect returns.

No doubt both Mint and Intuit will continue to benefit over the next few months as people count their pennies - both are expected to hit the one million mark for users soon.

But that still leaves an awful lot of business to fight over and it's probably fair to say Mint has won the first round in the publicity battle.

As one reader comment on the TechCrunch story put it: "Whoever greenlighted this letter did his investors a disservice. What great advertising for Mint! This will cause a lot of people to jump on the bandwagon."