If you plan to visit car dealerships this weekend, you may need to be more patient than usual. A cyberattack has disrupted software used by about 15,000 dealerships nationwide, slowing many car sales.

Not all dealerships are affected, and many of those impacted by the hack remain open. But their operations are slowed, with many returning to pen-and-paper processes while they wait out a solution to the attack.

Several Software Providers; Just One Impacted

Car dealerships today operate with the help of Dealership Management Services (DMS) software, which are computer systems that help manage inventory, process credit applications and payments, and generate sales contracts.

Related: Is Now The Time To Buy, Sell, Or Trade-In A Car?

Several companies sell DMS systems. The attack has affected only one major provider: Illinois-based CDK Global. Dealerships that use software from rival providers are unaffected.

CDK has told its customers the system could be down for several days, CNN reports.

While the company has stayed quiet about the nature of the problem, Security Week explains, “the attack’s highly disruptive nature suggests that it could involve ransomware.” An IBM study last year found that the average duration of a ransomware attack was 3.84 days.

Many Affected Dealerships Still Open

Weekends are traditionally important sales days for car dealers. Americans who work during the week tend to do their car shopping on Saturday and Sunday. So, few dealerships are willing to close their doors over a weekend.

Related: When Are The Best Times To Buy A New Car?

Instead, many are shifting to old-fashioned methods.

“My selling team can handwrite a buyer’s order,” Brian Benstock, general manager of Paragon Acura in New York, told CNN.

Craig Schreiber, who co-owns several dealerships near Buffalo, New York, told USA Today, “We are able to go ‘old-school’ as a result of our prior preparation, including the use of handwritten, manual forms in all of our departments.”

What You Can Do

With some dealerships running slower than normal, shoppers should be prepared.

Our recommendations:

• Call Ahead. There is no published list of CDK clients. Without calling ahead, you can’t know if a dealership you plan to visit might be affected. If you’re spreading your shopping across several days, you might benefit from visiting unaffected dealerships this weekend and saving test drives of cars at affected dealers until after the attack has been resolved.
• Allow More Time Than Normal. If a dealership you need to visit is impacted, be prepared for any transaction to take longer than usual. Most dealers can still check credit, accept payments, and generate contracts. But they will be forced to use slower-than-normal processes.
• Consider Shopping on a Weekday Instead. Weekends are the busiest days of the week for car dealers. If you come back during the week, you’ll have less competition from other shoppers, and dealers will have more time for you.

Cox Automotive, parent company of Kelley Blue Book and Autotrader, also owns CDK competitor Dealertrack.