Apple MacBook laptops and iMac desktop computers have a filter defect that causes trapped dust, leading to permanent screen smudges and sluggish performance, a proposed class action alleges.

Computer components generate heat during use. The technology giant installed cooling fans and vents but failed to include filters, the suit alleges. This “filter defect” causes the fans to suck in debris that gets stuck behind the screen, causing dark spots in the corners, it says.

Accumulated dust also causes computer motherboards to overheat, causing slowdowns and crashes, the plaintiffs allege in their suit in the U.S. District Court for the Northern District of California.

Apple, Inc. wasn’t immediately available for comment.

The company also faces litigation alleging it throttled battery performance of older iPhones with software updates.

Consumers who sought out-of-warranty screen repairs were told they had to spend at least $600 for a replacement even though the computer screens can be cheaply removed and cleaned, the suit says.

Dust accumulation is a well-known problem in the technology community, the suit says.

Apple computer owners have been complaining about smudge marks on their displays for years, according to the suit.

The problems persist after warranty repairs, because the replacement parts and computers have the same defects as newly purchased ones, the suit alleges.

Plaintiffs include a photographer who says the smudges on her iMac hampered her ability to work, a business owner who spent more than $600 to replace his iMac screen, and a Colorado man who paid for iMac two screen replacements and then $900 for a new motherboard.

The plaintiffs seek money damages on behalf of a class of all persons or entities who ever owned a MacBook, MacBook Pro, MacBook Air, iMac, or an iMac Pro.

Hagens Berman Sobol Shapiro LLP represents the plaintiffs.

The case is Ahearn v. Apple, Inc., N.D. Cal., No. 18-7196, complaint 11/28/18.