"Earlier this year the Metropolitan police received a number of allegations of denial of service cyberattacks against several companies by a group calling themselves Anonymous. We are investigating these criminal allegations and our investigation is ongoing," the Met said.
"The Metropolitan police service is monitoring the situation relating to recent and ongoing denial of service attacks, and will investigate where appropriate."
Mastercard, Visa and PayPal have all been victims of the attacks, which see hundreds of load requests bring the sites to a standstill. A group of online activists called Anonymous are thought to have launched the attacks in retaliation after MasterCard, Visa and PayPal withdrew support for donations to WikiLeaks as they were concerned that the website's activities were illegal.
WikiLeaks planned to publish around 250,000 sensitive US Department of State. However, so far only around 300 cables have been published, including some that link China to the attacks on Google at the beginning of the year.
Earlier this week, the UK's national security advisor, Sir Peter Ricketts, warned the Prime Minister that government websites could face similar attacks if WikiLeaks founder Julian Assange was extradited to Sweden, where he is wanted on one count of unlawful coercion, two counts of sexual molestation and one count of rape. However Assange was bailed on Tuesday.
At least three people, including two Dutch teenagers, have been arrested in the past week on suspicion of participating in the attacks. Most of those involved in the group are believed to be teenagers, based around the world, including in the UK.
However, WikiLeaks has distanced itself from the attacks.
"These denial of service attacks are believed to have originated from an internet gathering known as Anonymous. This group is not affiliated with Wikileaks. There has been no contact between any WikiLeaks staffer and anyone at Anonymous," said Kristinn Hrafnsson from the organisation, in a statement posted on the WikiLeaks website.