Police in the UK, US and the Netherlands have arrested more than 20 people as part of an investigation into major cyber attacks.
Most of the arrests were in the US, where the FBI said 16 people had been detained, 14 in connection with an attack on eBay's PayPal in December by hacking group Anonymous.
UK police, collaborating with the FBI and Dutch counterparts, arrested a teenager in London and four other suspected hackers were detained by police in the Netherlands.
The 16-year-old boy arrested in south London was detained on suspicion of breaching the Computer Misuse Act 1990, according to the BBC.
The attack is believed to have been in retribution for PayPal closing a donation account for Wikileaks.
Anonymous temporarily shut down MasterCard and Visa last December using a distributed denial of service (DDoS) attack. The attack was enabled by an open source computer program the group made available for free download on the internet, after the two financial companies froze Wikileaks accounts.
Anonymous targeted Amazon after it removed Wikileaks content from one of its servers, but that attack was unsuccessful.
The 14 suspects in the PayPal hack case were arrested in ten different US states. Authorities said the other two US suspects were being held on similar charges in Florida and New Jersey.
Authorities believe Anonymous is mostly made up of hackers in their teens and early 20s, according to US reports. Those arrested this week were aged between 20 and 42.