This action follows a large number of reports on the official PlayStation message boards of the update adversely affecting users' systems. The most widely noted problem is systems simply failing to reach the XMB upon booting, instead getting stuck on a screen with only the familiar "wave" background displayed.
Some posters have reported that removing the PS3 hard disk, formatting it via a PC, then re-inserting it allows the PS3 to boot properly ... with the obvious drawback of losing everything – profiles, saves, DLC, etc. – that was on the drive.
Joystiq contacted SCEA for comment on the situation as was told by PR director Patrick Seybold that they are aware of the message thread and that they are "looking into it right now and will work with those customers directly to address any issues they may be experiencing." This comment came before the update was removed from Sony's servers. We're seeking further comment and will update as we receive it.
Update: SCEA has issued a formal statement via the official PlayStation blog confirming that firmware 2.40 has "temporarily" been taken offline until it can "isolate the problem" and "identify a solution."