He had no terrorist sympathies or political ideologies - he was simply in it for the money.
His handbook, The Anarchist's Cookbook, took the form of two CDs that could be ordered from his website of the same name for US $35 (£24) a time.
Brown's website, which he used to sell the manual from his unremarkable terraced home, has since been removed from the internet by police.
The selling of his "cookbook" went on for five years between 2003 and 2008.
Brown pulled together information from a variety of sources to make his CDs, which contained thousands of pages of information.
As well as the al-Qaeda advice, the CDs included extracts from the Mujahideen Poisons Book and instructions on how to build improvised explosive devices
BBC News - Terror 'cookbook' writer from Portsmouth driven by cash
The lesson here is 'Be wary of what you are selling'
Brown told the jury during the three-week trial that he only did it to make money, that the information was freely available on the internet and that he had no sympathy with terrorists.
He was convicted of seven counts of collecting information that could have been used to prepare or commit acts of terrorism under the Terrorism Act 2000, two counts of selling and distributing the information under the Terrorism Act 2006 and a further count under the Proceeds of Crime Act.
Brown closed his eyes as the first guilty verdict was delivered by the foreman after less than four hours of deliberations.
The court heard that Brown had previously served a jail term for counterfeiting software.
Mr Justice Blair adjourned the case for sentencing at Winchester on Friday.
He granted Brown bail but warned him: "A custodial sentence of some length is inevitable given the gravity of these offences."