WESTPORT — “Check washing.”

It’s not money laundering. But police say it’s also dirty business.

And a growing number of check washing incidents has been reported recently in Westport.

Check washing, as described in a statement issued by Westport police, occurs when details on an already-written check — usually the amount and payment recipient — are erased and replaced with fraudulent information.

Most often, according to police, check washing is enabled when “checks that have been put in mailboxes and are awaiting pickup by a postal employee are stolen.”

After a check is stolen, erased and new details entered, the check is either cashed or deposited in a bank account controlled by the thief.

Checks have been stolen locally from both residential and U.S. Postal Service mailboxes, police said.

Instead, police recommend people avoid using free-standing mailboxes and complete transactions either electronically or putting checks in the mail directly at a post office.

Each of the recent check washing thefts is being investigated, police said.