A 21-year-old Syrian hacker, responsible for flooding 3,500 websites across the world with messages praising the Charlie Hebdo attackers, has been detained by the Bulgarian investigators.

The Bulgarian Chief Directorate for Combating Organised Crime carried out a raid on the house belonging to the Islamist hacker on 13 June, reported The Sofia Globe.

It is reported that the detained hacker, who migrated along with his family from Syria, has been residing in Bulgaria along with his parents for the last 20 years. The hacker is reportedly the member of MECA, which is the acronym for Middle East Cyber Army.

The group hacked into 3,500 government and corporate websites, and flooded the pages with messages in Arabic and English praising the Charlie Hebdo attackers, the Bulgarian ministry said in a statement.

The Bulgarian Interior Ministry is yet to release the identity of the detained man. It is understood that his name will be released only after the pre-trial proceedings.

The investigators claim that the 21-year-old used to communicate with other members of MECA through secure channels. The group would discuss plans and map out target websites before launching a full attack.

Following the raid on the suspect's house on Monday, the authorities seized computers and external storage devices containing high-tech hacking tools developed by the Syrian hacker, Shanghai Daily reported.

In the wake of the Charlie Hebdo attacks in Paris, Islamist radicals were blamed for hacking into 20,000 websites across France, belonging to newspapers, restaurants, schools, libraries, and even local waste-management departments.

The hackers put up the black Islamic flag on websites with messages in Arabic and English saying: "The Islamic State Stay Inshallah, Free Palestine, Death to France, Death to Charlie."