I'd first start with talking to who ever is in charge of the office computers and finding out if they have any network protection and what is provided to client computers. I've seen not soo smart small businesses run openly and are just a perfect target to lose everything.
If you have a good anti-virus that doesn't provide malware protection ThreatFire could help do the trick. I like MalwareBytes though unless you pay for the full version you do not have realtime protection. And if you do not have antivirus get Avast free version and you should be set.