Since it became the default URL shortener for Twitter, Bit.ly has been growing like crazy. And as we learned from Spider-Man, with great power, comes great responsibility.

Bit.ly has started warning users of potentially malicious sites, based on information it has about URLs being shortened. For example, if you click on this link, you’ll see the message that reads, “Warning – this site has been flagged and may contain unsolicited content. The content of this web page appears to contain spam, or links to unsolicited or undesired sites.” It then gives the following suggestions:

Close your browser window

Notify the sender of the URL

Or you can also continue on to the link, at your own risk, if you click another URL on the page.

And this do-gooding likely plays into Bit.ly’s greater plans to become a more Digg-like destination for content.

Bit.ly is apparently pulling this malicious site info from StopBadware.org and antiphishing.org, just as many other services do.

[thanks Adam via tunese]