Fingerlings, those colorful chirping monkeys (and sloths and unicorns) that wrap around your finger, have become one of the most desired toys on holiday shopping lists.

Unfortunately, the $15 creatures are sold out online almost everywhere. Toys 'R' Us? Gone. Walmart? None left in stock. Target? Nope. But check eBay or Amazon, and sellers are offering them for double, triple and quadruple their original price.

Hot holiday toys have always been hard to find. Think Cabbage Patch Kids dolls in the 1980s. But the proliferation of online shopping makes it even tougher to purchase coveted items because of software that snaps them up as soon as they are offered for sale.

"If it's popular, it's going to be taken by bots and resold," said Omri Iluz, the co-founder and chief executive of the cybersecurity firm PerimeterX. The bots work by constantly pinging retail websites, searching for sales and analyzing URLs.

The moment an item is in stock, the software runs through the checkout process at a speed that is "completely inhuman," said Iluz, whose company protects large retailers from bot attacks.

Amazon said Tuesday that it monitors bot buying activity, and attempts to limit the purchase of high-demand products.

Target has also taken measures to deter resellers, said company spokesman Eddie Baeb, "including quantity limits for purchases and technologies designed to help us monitor and prevent reseller activity."

Senate Minority Leader Chuck Schumer has asked retail trade associations to take action. Unusual purchases, for example, ought to raise a red flag, said Schumer spokesman Angelo Roefaro.

Schumer co-sponsored the Better Online Ticket Sales Act, or BOTS Act, which was signed into law last December, and is targeted at online ticket scalpers. The law makes it illegal to bypass ticketing website security measures, and would fine hackers who seek to circumvent the system.

Sen. Richard Blumenthal, D-Conn., a cosponsor of the BOTS Act, said he aims to introduce legislation to combat the "plague" of bots that buy up toys, sneakers and other popular retail items. "I think if there was a specific law it would encourage and empower the Federal Trade Commission or criminal investigators to go after them, and we might learn more about them and identify some of the specific culprits," he said.

Caron writes for the New York Times.