Nine people have been detained on suspicion of hacking government and military websites, Deputy Prime Minister and Defence Minister Prawit Wongsuwon said on Monday.
Authorities also seized computer and accessory equipment, Gen Prawit said. More arrests could be expected.
"Authorities are not turning a blind eye. I assure you that we are taking action," he said.
National police chief Chakthip Chaijinda on Monday paraded one of the detained suspects before the media at the police head office in Bangkok. The 19-year-old man was identified as Natdanai Khongdee. He was allegedly in possession of two pistols, a rifle, two gun frames, ammunition and marijuana when apprehended.
Pol Gen Chakthip said Mr Natdanai was one of many young people influenced by an internet-based group, identified as "opsinglegateway", into attacking government websites.
The teenage suspect was knowledgeable about technology but had dropped out of a technical college in Khlong Sam Wa area of Bangkok.
Most of the people influenced by the group were 17-20 years old. They were given false information, that the new Computer Crime Act would lead to a single internet gateway, according to Pol Gen Chakthip.
"The group has been active since Dec 17," he said, adding, "The website of the Royal Thai Police Office was hacked and crashed. Three days later the suspect was arrested."
The National Legislative Assembly passed the amended Computer Crime Bill on Dec 16.
The amended act had nothing to do with the single internet gateway idea, it only modernised 2007 regulations to meet the challenges of a rapidly changing world of computer-related technologies, the police chief said.
Police also alleged that Mr Natdanai had traded in guns over the internet.
Pol Gen Chakthip said the military had arrested the suspected hackers. Mr Natdanai had been handed over to police for prosecution. He did not elaborate on the place and time of the arrests.
It was not made clear how many were handed over to police and how many were still in military detention.
The police chief said the "commanders" of the opsinglegateway group were both inside and outside the country.
He declined to say how many people were involved or if they were connected with any political group.
Pol Maj Gen Siripong Timula, head of the police Information Technology Support Division, said there were many sub-groups of hackers working for the opsinglegateway group and there were several levels of sub-groups.
Mr Natdanai had attacked only the outer level of the Royal Thai Police Office website, he said.
Tourism and sports permanent secretary Pongpanu Sawetrunon said he had filed a complaint with Nang Loeng police station in Bangkok against the so-called Anonymous hacker group, for attacking the website of the ministry, www.mots.go.th, late on Friday night.
He said even though the attack was minor and symbolic it caused the website to be unusable. Officials were still unable to update information on the homepage, and this affected people’s right to information.
Experts from the Electronic Transactions Development Agency (ETDA) would strengthen the ministry's website security against any future attacks, he added.