UPDATE #2: EA has issued permanent bans to players it found using the FIFA 13 Ultimate Team exploit, detailed below.
The FUT 13 web app is also now back online.
"Yesterday, a very small number of users attempted to gain an unfair advantage on the FUT web app," EA announced via its FIFA 13 Twitter account. "The FUT13 Web App had to be taken offline to be stabilized and ensure a level playing field for all FUT users.
"Permanent bans for FIFA 13 FUT have been served to all users who attempted to gain an unfair advantage. Thanks for your patience while we create the best experience for all fans of FUT."
Questions remain about the long-term impact of the exploit upon the game's economy, as well as why the issue was allowed to happen for a second year running. We've put these questions to EA and will update when we hear back.
UPDATE: EA has told Eurogamer it is investigating the reports, and re-iterated the statement released on the official FIFA 13 Twitter this morning:
"Our team is still working on providing a stable experience for the #FUT13 Web App," the message read. "Thanks for your patience. More details when we have them."
An earlier message admitted that the team had "identified some new issues that are affecting user experience".
ORIGINAL STORY: FIFA 13 Ultimate Team players have reacted angrily to a browser exploit that allowed some people abundant access to restricted packs of football player cards.
The unscrupulously-gotten football stars were then being sold on for lots of profit, making the exploiters rich and flooding the market with stars like Messi and Ronaldo.
The exploit pertains to the FIFA 13 Ultimate Team web app, which has now been taken offline.
EA's official FIFA 13 forum was flooded with messages about the issue. Many people berated EA for lack of information or response to the scam.
Users are concerned that although the people unlocking these packs can be traced and banned, the ill-gotten players they've sold on will remain - thus putting the game's economy in flux.
Some people are calling for a worldwide server rollback to before the exploit caught on.
Worryingly, and without going into too much detail for obvious reasons, the exploit appears to be achievable with even basic-level computer savviness.
More concerning still, a quick Google search shows the same exploit was a problem last year, and affected FIFA Ultimate Team 12.
EA currently lists the FIFA Ultimate Team 13 web app as "offline for maintenance".
Eurogamer has contacted EA to find out what it is being done to combat the issue. We'll update you when we hear back.