Abstract: When a user successfully logs into an account, the user is provided with a first-class login token, which entitles the user to one or more unsuccessful login attempts without experiencing delays the user would otherwise experience. If attempts with a second-class login token or an expired first-class login token is impermissible, a subsequent login attempt is subject to delays the user would otherwise not experience. The delays minimize the effectiveness of dictionary attacks. Additionally, if the user attempts to login without a login token or an invalid login token, the login attempt is impermissible and the user is provided with a second-class login token for use in a delayed, subsequent login attempt.

Abstract: When a user successfully logs into an account, the user is provided with a first-class login token, which entitles the user to one or more unsuccessful login attempts without experiencing delays the user would otherwise experience. If attempts with a second-class login token or an expired first-class login token is impermissible, a subsequent login attempt is subject to delays the user would otherwise not experience. The delays minimize the effectiveness of dictionary attacks. Additionally, if the user attempts to login without a login token or an invalid login token, the login attempt is impermissible and the user is provided with a second-class login token for use in a delayed, subsequent login attempt.

Abstract: Provided is a computerized method for monitoring the content of documents. A set of documents is stored in memories of server computers. The server computers can be connected to each other by a network such as the Internet. Entries are generated in a search engine for each document of the set. The search engine is also connected to the Internet. The entries are in the form of a full word index of the set of documents. The search engine also maintains a first abstract for each document that is indexed. The abstract is highly dependent on the content of each document. For example, the abstract is in the form of a sketch or a feature vector. Periodically a query is submitted to the search engine. The query locates a result set of documents that satisfy the query. A second abstract is generated for each document member of the result set. The first and second abstracts are compared to identify documents that have changed between the time the set of documents were indexed and the time the result set is generated.