Users of the popular money transfer app are getting a warning from Denver Police: watch your phones! People are going into the app and transferring money to their bank accounts, law enforcement says.

Venmo is an app that lets you transfer money between you and a friend's bank account. You put your bank account information in the app and it automatically pulls the money as soon as you initiate a transfer. Transferring itself is very easy and can be done in seconds.

Which leads to the situation where scammers are getting away with people's money: they'll go to a bar or restaurant, find Venmo users, steal that person's smartphone and then use the app to transfer money.

Police have some advice for Venmo users: keep your phone and belongings close to you at all times; don't make use of Venmo public or talk to strangers about it; don't give your phone unlock code out to anyone - and don't make your code your date of birth or some other easily found out number.

So far, authorities have gotten 13 calls from people who've been scammed this way.