Update: Microsoft has sent us the following statement:

“We do not have any evidence the Xbox LIVE service has been compromised. We take the security of our service seriously and work on an ongoing basis to improve it against evolving threats. However, a limited number of members have contacted us regarding unauthorized access to their accounts by outside individuals. We are working with our impacted members directly to resolve any unauthorized changes to their accounts. As always, we highly recommend our members follow the Xbox LIVE Account Security guidance provided at www.xbox.com/security to protect your account.”

This seems to be a rather amazing response, considering the amount of people who have contacted us with their own experiences since this story has been published. The original story begins below.

Ars Technica has received a number of reports from Xbox Live customers complaining about hacked accounts, unauthorized purchases, and a slow response from Microsoft itself. The pattern is weirdly specific: gamers notice that unauthorized purchases have been made using their credit card information or existing points, and FIFA Soccer 11 or 12 has been played on their account.

"Yesterday, my live account got hijacked and charged just over $100. Specifically, two large purchases of points followed by the download of FIFA 12, which had 2 achievements unlocked for the game, and every MS point spent on Gold Premium Packs and DLC," one reader wrote. His Xbox was turned off, and he learned of the breach from confirmation e-mails sent to his workplace.

Another gamer blogged about his account being breached:

"Sure enough, all of the Microsoft points that were stored in my XBL account had been spent on in game items for FIFA 11(I don’t own that game hell, I don’t even like soccer video games) and whoever spent my MS points had then tried to purchase more. Presumably, when that purchase failed, they abandoned my account and went on to steal from some other unsuspecting gamer."

These online reports are becoming increasingly common, and Microsoft's response has been to lock down affected accounts for 25 days while the company investigates the charges. We've e-mailed Microsoft for comment, and have yet to hear back. For now, the best course of action is to keep a close eye on your account, and contact Microsoft if you see any fraudulent charges or notice FIFA-related activity in your achievement points or history.