Schools have become magnets for ransomware.

The number of schools hit by ransomware ticked up in September growing to roughly twice the number in August, according to cybersecurity firm Emsisoft.

Emsisoft provided Fox News with a list of about a dozen schools that have already fallen victim to attacks in September.

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Two of the highest-profile attacks this month have been Hartford public schools in Connecticut and Fairfax County Public Schools in Virginia – the latter the 10th-largest school division in the country.

A man types on a computer keyboard in Warsaw in this Feb. 28, 2013, illustration file picture. (REUTERS/Kacper Pempel/Files)

A ransomware attack in some cases shuts down a school's computer systems, which can effectively shut down the school, as happened to Hartford public schools earlier this month. Criminals typically try to lock down systems while threatening to steal student information and sensitive administrative documents. Then a ransom is demanded in order to stop the attack.

“The September uptick can mostly be attributed to the fact the public sector is gradually reopening -- after the summer break in the case of schools -- so more people are working in-office and opening emails,” Brett Callow, a spokesperson for Emsisoft, told Fox News.

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“An aggravating factor was the emergence of a type of ransomware called Conti in July,” Callow said. Conti has been linked to Ryuk, a group that has a long history of attacking schools and public sector entities.

The biggest concern for schools is the emergence of a pattern, meaning it could get worse in the coming months.

“With the news that Fairfax County public schools in Virginia were hit with ransomware in the first week of the new school year, a series of unfortunate incidents is no longer random, but appears to be a pattern,” Sophos Principal Research Scientist Chester Wisniewski told Fox News.

“I fear we are seeing a new trend in ransomware gangs sharpening their tools to attempt to apply more pressure on [schools],” Wisniewski said.

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Schools are considered soft but lucrative targets because they often have outdated computer systems but have access to cash.