The digital trove of credit card numbers and emails stolen by the group known as Anonymous came from towns across rural America places like Gassville, Arkansas and Tishomingo County, Mississipi, where officers don't usually have to worry about international hackers.

That may have made them an easy score. The loosely knit hacking collective said on Saturday that it attacked 70 mostly rural law enforcement websites in the United States in retaliation for the arrests of its sympathisers.

Some county sheriffs said they were told about the hacking, but others appeared to learn of the scope of what had happened only when contacted by The Associated Press. 

Web security experts said the cyber attack shows that no website is too small to avoid hacking, especially as more law enforcement agencies upload sensitive information about investigations, inmates and officers to their sites.

"It seems to me to be low-hanging fruit," said Dick Mackey, vice president of consulting at Sudbury, Massachusets-based System Experts. "The smaller the organisation, the more likely that they don't think of themselves as potential targets. They're not going to have the protections in place that a larger organisation will have."

Many of the sheriff's offices outsourced their websites to the same Mountain Home, Arkansas-based media hosting company, Brooks-Jeffrey Marketing. If Brooks-Jeffrey's defences were breached, that would give hackers access to every website the company hosted, said Kevin Mitnick, a security consultant and former hacker.

Brooks-Jeffrey declined to comment. Most of the sheriffs' department sites, if not all, were either unavailable for most of yesterday or had been wiped clean of content. Some had started to reappear online yesterday evening.

The emails were mainly from sheriffs' offices in Arkansas, Kansas, Louisiana, Missouri and Mississippi. Many of the leaked emails appeared to be benign, but some of the stolen material seen by the AP carried sensitive information, including tips about suspected crimes, profiles of gang members and security training.

At least one email had material including pictures of teenage girls in their swimsuits that Tim Mayfield, the police chief in Gassville, Arkansas, said was sent to him as part of an ongoing investigation. Mayfield declined to provide more details.