As usual, here is the list of the main cyber attacks for April 2012. A first half of the month which has been characterized by hacktivism, although the time of the resounding attacks seems so far away. Also because, after the arrest of Sabu, the law enforcement agencies (which also were targeted during this month, most of all in UK), made two further arrests of alleged hackers affiliated to the Anonymous Collective: W0rmer, member of CabinCr3w, and two possible members of the infamous collective @TeaMp0isoN.
Update June 29: 2011 Cyber Attacks (and Cyber Costs) Timeline (Updated)
I found this interesting graph from an original Thomson Reuters post, showing the timeline of the major 2011 CyberAttacks.
The graph shows all the main Cyber Events of this tremendous 2011 up to June, the 16th. Actually to be perfect it should include also the infamous Epsilon Data Breach, happened on March, the 30th. Probably it had a major impact on the U.S. rather than in Europe, but it is clear that the aftermaths of this breach will last for years in terms of spear-phishing attacks tarteting the affected users.