SEATTLE (AP) _ Thieves are finding new ways to steal mail now that the Postal Service has installed high-security mailboxes _ they're smashing the boxes open with cars and sledgehammers.

Six of Seattle's new theft-resistant blue streetside mailboxes fell victim to the thieves over the weekend.

Four of the boxes were ripped off of their concrete pads and hauled away. Two others were ``beaten to a pulp'' with crowbars or sledgehammers, but withstood efforts to break into them, Postal Service Inspector Jim Bordenet said.

Postal workers began working last month on a $2 million program to replace 3,500 blue mailboxes stretching from Everett to Tacoma. Thieves had obtained a master key to them, and reports of lost credit cards and checks had skyrocketed. One man recently convicted of possessing checks he stole from Seattle mailboxes told authorities he was part of a ring of 30 bandits who used the keys to conduct nightly box raids.

Although they admitted the boxes weren't safe, postal authorities at first said it would take years to fix the problem. But after a public outcry, the agency stepped up its efforts to correct the problem, adding brass padlocks to 90 percent of the old boxes in Seattle until the boxes could be replaced.

The new boxes are made of heavy-gauge metal and have a wider lip and added pins on the door to stymie any attempts to pry open the doors. The boxes also are bolted to the pavement with two different bolts, and each box is fitted with a hardened-steel lock with a counterfeit-proof key.

Word of the attacks on the new boxes dismayed and frustrated neighborhood residents.

``I guess I was pretty upset with the post office's initial reaction to the mail theft problem _ that they'd get it fixed within a year or so,'' said Allen Sinear, who lives just a few doors from one of the mailboxes hit early Sunday.

``But it is kind of hard to know what they should be doing with these kind of tactics,'' he said.

Sinear said he thinks the noise involved in ripping the mailboxes off of their bases eventually will trip up the thieves.

``My guess is that somebody couldn't get away with that too many times without getting caught,'' Sinear added.