What do the IMF, Citibank, Sony and now Sega all have in common? In a span of just a few weeks, all of these companies, and more, have joined the ranks of those firms fallen victim to cyber crime.

Sega said issued a warning to users on Friday that personal data may be at risk after being infiltrated.

Passwords were encrypted and no financial data was accessed, it said.

Sega joins a growing list high profile company's that have been hit in recent weeks by cyber crime.

On Wednesday the public website of the CIA went down, with the hacker group Lulz Security saying it had launched the attack.

Although the group fashions itself more as pranksters and activists than people with sinister intent, its members have been accused of breaking the law and are wanted by the FBI and other law enforcement agencies.

Lulz broke into a Senate website over the weekend and released data stolen from the legislative body's computer servers.

In May, the group posted a fake story on the PBS website saying that rapper Tupac Shakur was still alive and living in New Zealand.

The group denied any involvement in the Sega case,  however, asking Sega to instead contact them to help destroy the hackers that attacked you.

But it does underline mark an uptick in crime over the Internet

The last high-profile victim was the International Monetary Fund this weekend, who's computer network was breached by what was believed to be a government backed effort.

Just last week banking giant Citibank confirmed that credit card data of about 200,000 of its North American customers have been hacked. The event marked the largest attack on a bank in the US to date.

The week before US military contractor Lockheed Martin was compromised as hackers used Lockheed's own secure id technology to access its networks.

Google has accused Chinese hackers of targeting the Gmail accounts of U.S. government officials.

The Sega Pass system was taken offline on Thursday and all users' passwords have been reset. Customers have been advised to be on the alert for suspicious emails asking for further personal information.

The hacking group Lulz Security appeared to deny involvement, despite leading a wave of recent cyber-attacks such as that on Sony. A tweet using the account @LulzSec said: @Sega - contact us. We want to help you destroy the hackers that attacked you.

In April, Sony had data stolen from the 77 million users of the PlayStation network, one of the worst security breaches of its kind. There was then a second attack when another 24.6 million computer game users might have had their personal details stolen.

Personal information and passwords were taken in another hack on Codemasters earlier this month, but not financial details.

The email from Sega to customers said: We have identified that unauthorised entry was gained to our Sega Pass database. We immediately took the appropriate action to protect our consumers' data and isolate the location of the breach. We have launched an investigation into the extent of the breach of our public systems.

We have identified that a subset of Sega Pass members emails addresses, dates of birth and encrypted passwords were obtained. To stress, none of the passwords obtained were stored in plain text.

Please note that no personal payment information was stored by Sega as we use external payment providers, meaning your payment details were not at risk from this intrusion.