1. A method of employing social media data to improve accuracy of risk-based authentication, the method comprising: observing, on a continual basis by processing circuitry of a posting extraction device, postings aggregated in a social media forum, said observing including (i) sending, by the posting extraction device, social media access requests to the social media forum to access a set of postings on the social media forum and (ii) searching, by the posting extraction device, the set of postings to identify a user post of a poster, the user post containing any of a set of keywords, each of the set of keywords having a specified impact on a risk score; extracting, by the posting extraction device, data from the observed postings, the data including posting data from the user post, the posting data including discontinuous event data that includes at least one of the set of keywords and a time when the user post was made; and assigning, by a risk-based authentication server, risk scores to a set of electronic transactions based on the extracted data, the risk scores being indicative of a risk of fraud in the set of electronic transactions, wherein assigning the risk scores includes, for a particular risk score, (i) computing a first risk score component based on a previous electronic transaction, (ii) computing a second risk score component based on the discontinuous event data, and (iii) producing the particular risk score based on the first risk score component and the second risk score component, wherein the method further comprises: storing the posting data from the user post in a transaction database in connection with a user identifier of the poster and further in connection with transaction history information of the poster; receiving, by the risk-based authentication server after the user post was made, a request to authenticate an electronic transaction, the request to authenticate specifying the user identifier of the poster and a time when the request to authenticate is made; and in response to the risk-based authentication server determining (a) that the time when the user post was made is more recent than any prior electronic transaction associated with the user identifier in the transaction history information and (b) that the posting data from the user post contains at least one of the set of keywords, (i) assigning a high risk score to the electronic transaction and (ii) preventing the electronic transaction from going forward.
1. A method of employing social media data to improve accuracy of risk-based authentication, the method comprising: observing, on a continual basis by processing circuitry of a posting extraction device, postings aggregated in a social media forum, said observing including (i) sending, by the posting extraction device, social media access requests to the social media forum to access a set of postings on the social media forum and (ii) searching, by the posting extraction device, the set of postings to identify a user post of a poster, the user post containing any of a set of keywords, each of the set of keywords having a specified impact on a risk score; extracting, by the posting extraction device, data from the observed postings, the data including posting data from the user post, the posting data including discontinuous event data that includes at least one of the set of keywords and a time when the user post was made; and assigning, by a risk-based authentication server, risk scores to a set of electronic transactions based on the extracted data, the risk scores being indicative of a risk of fraud in the set of electronic transactions, wherein assigning the risk scores includes, for a particular risk score, (i) computing a first risk score component based on a previous electronic transaction, (ii) computing a second risk score component based on the discontinuous event data, and (iii) producing the particular risk score based on the first risk score component and the second risk score component, wherein the method further comprises: storing the posting data from the user post in a transaction database in connection with a user identifier of the poster and further in connection with transaction history information of the poster; receiving, by the risk-based authentication server after the user post was made, a request to authenticate an electronic transaction, the request to authenticate specifying the user identifier of the poster and a time when the request to authenticate is made; and in response to the risk-based authentication server determining (a) that the time when the user post was made is more recent than any prior electronic transaction associated with the user identifier in the transaction history information and (b) that the posting data from the user post contains at least one of the set of keywords, (i) assigning a high risk score to the electronic transaction and (ii) preventing the electronic transaction from going forward. 8. The method as in claim 1 , wherein computing the first risk score component includes: obtaining previous values of a transaction factor associated with the user identifier; obtaining a new value of the transaction factor from the request to authenticate the electronic transaction; and producing, as the first risk score component, a number indicating a likelihood that the transaction factor would have the new value given that the transaction factor has had the previous values, wherein each of the observed postings includes metadata, the metadata including values of posting parameters; wherein computing the second risk score component includes: extracting the metadata of the observed postings; accessing the values of the posting parameters from the metadata; and producing, as the second risk score component, a number indicating a likelihood that the electronic transaction is fraudulent based on the values of the posting parameters, and wherein producing the particular risk score based on the first risk score component and the second risk score component includes forming a sum of the first risk score component and the second risk score component.