Liz Weston

Dear Liz: I recently got an email from my credit card issuer stating my credit score had just dropped 21 points. Having a good credit score and not aware of any recent adverse actions, my first reaction was alarm.

Checking with the issuer online, I saw only advertisements for “protect your credit” services, so I phoned. I was informed the numbers came from Equifax credit bureau. I contacted Equifax as well as TransUnion and Experian, which resulted only in more offers of products to protect my credit. I downloaded my free credit reports from AnnualCreditReport.com and found nothing suspicious. I was finally directed to FICO, but an email sent more than a month ago remains unanswered.

Is it legal for these companies to market their products through presumably fictitious or even fraudulent means? What is the best way to find out my true credit score? Can my credit score suffer because I ask these questions in a public forum?

Answer: Knowing a little more about how credit scoring works may put your mind at ease.

There is no one “true” credit score. Lenders and other companies use many different kinds. FICO is the leading credit scoring company and the FICO 8 is the most commonly used score, but many companies use older versions or ones modified for their specific industry (such as the FICO Auto Score 5, for example). Plus, your FICO 8 from Experian may be different from your FICO 8 from TransUnion or Equifax because the scores are based on the information in your credit bureau files and the bureaus are separate, competing businesses that don’t always have the same information.

Then there’s the VantageScore, a rival to the FICO, which is used by some lenders and by many sites that offer people their credit scores for free. The VantageScore formula is different from the FICO formula, so your numbers could be different as well.

All these credit scores, however, are created solely using the information in your credit reports. Your income, gender, address, political opinions, computer operating system and online comments are not included in credit score calculations.

Some people are understandably confused about that. Various start-ups and researchers have suggested that non-credit information — such as information gleaned from someone’s social media postings or online surveys — could replace credit information in loan decisions. But the U.S. has fair credit reporting laws that probably would make such alternatives unworkable. (It would be nice if start-ups checked to see what regulations apply to their industry before sending out press releases, but that doesn’t always happen.)

Given that you didn’t see anything obviously wrong on your credit reports, you don’t need to worry too much. The credit score drop you describe might be because you charged more on a credit card than usual, had a credit limit lowered or applied for a bunch of credit in a short period of time. It probably will reverse itself over time.

Alerting you to credit score changes isn’t an illegal practice, even if the company’s primary purpose in keeping you up to date is to market credit-monitoring services to you. (Credit protection is a misnomer because these services can’t prevent identity theft. They can only alert you if it’s already happened.)

You did exactly what you should have done when you were alerted to the point drop — you went to AnnualCreditReport.com and checked your credit reports. If you want to put your mind further at ease, consider freezing your credit, a process that could prevent identity thieves from opening new accounts in your name.