RC4 encryption algorithm is widely used with HTTPS protocol. Though it is vulnerable to attacks that can break the encryption in reasonable time like RC4 NOMORE site explains.
What countermeasures should be taken? Quoted from the RC NOMORE site:
The only good countermeasure is to stop using RC4. Nevertheless, we did observe that generating the required amount of traffic can be a bottleneck when executing the attack. Hence attacks can be made more expensive, though not prevented, by making it more difficult to generate traffic. One option is to prohibit browsers from making parallel connections when using RC4 (normally multiple connections are made to load websites faster). This reduces the speed at which clients can make requests, meaning they generate traffic more slowly. However, we stress that this would only increase the execution time of attacks, and not prevent them.