The latest greatest swindlers in the cybercrime racket know you’re onto their digital three-card monte, and they’ve made a few adjustments, putting yet another wrinkle in the corporate-hacking game by targeting top-level employees for major profits.

These hackers appear to be based in North America or Western Europe, and they know a great deal about the companies and industries they’ve been cracking. They could be “white-collar hackers” or just good studies of character. It really doesn’t matter. Here’s what counts: They are hatching schemes so nuanced you may not see the hack that takes out your company till the smoke clears.

These hackers may have worked for your company, or one like it. They are going to know how your teams communicate. They’ll use the lingo and shorthand that you see every day. Emails may be super simple, like, “I need another pair of eyes on this spreadsheet about [term of art only people in your business would know].” They may know what you are likely to be talking about after certain kinds of industry news releases, and they’ll have a good idea of what times of day get busy for you so that you are more distracted and less likely to think before you click.

“The attacks are becoming much more sophisticated than anything we’ve seen before,” says Jen Weedon, a threat intelligence officer at the Silicon Valley-based cybersecurity firm FireEye.

The New York Times reported this week about one such group of hackers targeting senior executives at biotech companies with a goal of garnering insider information to game the stock market.

FireEye has been tracking the group, which they call Fin4—for a year and a half. (The “Fin” designation is assigned by the company to indicate groups where the main goal is to monetize proprietary information.)

“Fin4 has reached a threshold of capability that sets them apart,” Weedon told me during a phone conversation. “They are very thoughtful about who they target. They go after specific companies and are a lot more scoped in their approach.”

Attacks of this kind may start with the studied e-impersonation of trusted colleagues, business associates or anyone from a constellation of contacts—compliance officers, regulators, legal or financial advisers—with the single purpose of getting someone in a senior position to personally, unwittingly hand over the keys to the castle. Once they are in, sensitive—potentially lucrative—information can be accessed and put to use.

“They will send a very convincing phishing email,” Weedon said. “It may prompt a link that looks just like Outlook.” The target enters their credentials to see the attachment, not realizing that they were not in Outlook at all. There may even be a legitimate document on the other side of that fake login page, but it’s a trap. Once the hacker gets into a key person’s inbox, Outlook settings have been reset to send any messages containing the words “hacked” or “malware” directly to the user’s trash folder, thereby giving the cyber-ninja more time in the system to collect information about mergers and acquisitions, compliance issues, press releases, non-public market-moving information—anything that can be used to make a smarter stock market trade.

According to Weedon, the group has been able to infiltrate email accounts at the CEO level.

Once they’ve gained access, the hackers may simply collect everything in the CEO’s inbox or take an attachment found there and plant malware that then spreads throughout the company thereby exposing still more information. The difference here is that the hack relies on legitimate credentials to gain access, so it’s a much lighter touch with potentially much more information being comprised. If the hackers forgo malware, there aren’t necessarily any traces at all of the compromise.

The “old” way these breaches worked—one still very much practiced by Chinese and Russian groups—involved the use of general information, kinda-sorta knowledge of the target’s business and hit-or-miss English. Because there is often less specificity and more variables in these kinds of softer attacks, the dodge is easier to spot. It’s more likely to find a lower-level employee falling for it. In most cases, these targets don’t have the kind of access to information that can cause major damage. Having gained whatever access is possible through their mark, old-school hackers move laterally into the organization’s environment, whether by recording keystrokes to exploit privileged employee credentials or blasting a hole in the company firewall. They might as well be Bonnie and Clyde robbing a bank. The goal is to siphon off information that can be turned into an easy profit, but the process leaves traces.

What’s so worrisome about Fin4 is that they can come and go—gaining access to everything and anything pertaining to your company—and you may never know it. For the numerous healthcare and biotech companies that they targeted, the only real-life consequence could be an advantageous trade that somehow anticipated the announcement of a new drug, or shorted a stock associated with a failed drug trial.

If you are the target of choice, you will have to be exceptionally well trained by a cutting-edge information security professional and completely tuned in to the subtleties of your workflow to avoid getting got. These fraudsters will have at their fingertips the kinds of information that only an insider should know, and the bait they dangle in front of you will be convincing.

While the art is very different, the basic mechanism is the same. Company-killing compromises require human error. While more common hacks rely on a weakest link that can be exploited, the more hackers evolve, the more we all must evolve with them.