Apple is recalling a "very small number" of Seagate-made internal 1TB hard drives fitted in 21.5in and 27in iMacs sold earlier this year.
The machines shipped between May and July. Some of the drives have failed, prompting the recall.
Apple said it will replace the drives free of charge, though you'll have to take your machine in, and you do need to back up all your data first.
There's a page on Apple's website with more details.
Seagate drives on Macs have come under fire before, most notably in 2007 when China-made Seagate 2.5in HDDs were found by UK data recovery service Retrodata to hava a significantly higher failure rate than similar products from other suppliers.