In June 2007, Google Safe Browsing API was released, and last year, Google updated the API to version 2.0, along with a reference implementation in Python.
"The v2 provides more efficient updates compared to version 1, giving clients the most useful (freshest) data first. The v2 uses significantly less bandwidth, and also allows us to serve data that covers more URLs than previously possible. Browsers including Chrome and Firefox have already migrated to v2," Google informed.
Considering the above facts, Google today announced that the "discontinuation of v1 on December 1, 2011, along with the service take down thereafter."
"If you're currently using v1, you need to migrate asap to v2. In addition to the documentation and reference implementation, there's a Google Group dedicated to the API where you may get additional advice or ask questions as you prepare to transition," Google suggest.
"If you're worried about the complexity of the v2, we now have a lookup service that you can use in lieu of v2 if your usage is relatively low. The lookup service is a RESTful service that lets you send a URL or set of URLs to Google and receive a reply indicating the state of those URLs. You can use this API if you check fewer than 100,000 URLs per day and don't mind waiting on a network roundtrip. This process may be simpler to use than v2, but it's not supported for users who'll generate excessive load (meaning that your software, either your servers or deployed clients, will collectively generate over 100,000 requests to Google in a 24-hour period)," noted Google.
[Source: Google Online Security Blog]