First all, when new upgrade themes and plugin release, please update as soon as possible so that the bug and whole will be fixed.
Secondly, install anti spyware or firewall and scanner so that it scan and fix. If it is infected, some software remove it or fix it. But, the cost will be higher than the basic feature software.
Thirdly, hire specialist, who can fix it.
If you don't fix it in time, the service might be interrupted.
And, paid service is sometime worthy and get benefit, saves time and efforts than the free themes and plugins.