Blockchain token based projects need network effects. There needs to be a mechanism for fairly and widely distributing tokens to in order for the project to function well upon launch. A popular method thus far has been to sell those tokens in advance to prospective users of the network that are interested in crowdfunding its development. Another, lesser known, strategy is an “airdrop.”
In an airdrop, a project’s creators can take a snapshot of a public blockchain, such as Bitcoin’s or Ethereum’s, and send tokens to all wallet addresses containing some number of bitcoin or ether at the time the snapshot was taken. This requires no action on the recipient's part other than to take whatever steps are needed to take control of the tokens once they have been gifted. It can be a way to jumpstart a community by instantly putting tokens in the hands of a lot of people with a proven level of cryptocurrency savvy.
This seems like something totally new and unique to token projects, right? Not really. It turns out people have tried airdropping before, but with stocks. And the SEC did not look favorably upon the tactic. See this 1999 press release:
In each of the four cases, the investors were required to sign up with the issuers' web sites and disclose valuable personal information in order to obtain shares. Free stock recipients were also offered extra shares, in some cases, for soliciting additional investors or, in other cases, for linking their own websites to those of an issuer or purchasing services offered through an issuer. Through these techniques, issuers received value by spawning a fledgling public market for their shares, increasing their business, creating publicity, increasing traffic to their websites, and, in two cases, generating possible interest in projected public offerings.
So, since the SEC has found that some tokens can be securities, if you are considering using an airdrop token distribution be warned that even giving away tokens is not necessarily free from scrutiny under securities law.