The Internal Revenue Service has been added to a long list of companies and government agencies that hackers have breached in the last year.

And so, if there is any advice security experts have for those trying to keep their personal information safe, it is simply: You can’t.

“Your information has already been out there for years, available to anyone who wants to pay a couple dollars,” Brian Krebs, a security blogger who has been a frequent target of hackers, said Wednesday.

The attack on the I.R.S. is just the latest evidence that hackers already have all the information necessary to steal your identity. The agency said Tuesday that hackers used information stolen from previous breaches — including Social Security numbers, birth dates, street addresses and passwords — to complete a multistep authentication process and request tax returns and other filings.