【正确答案】[译文]最初，问题(主要)是个人电脑失窃；由于大部分电脑安装在办公室里，而过去办公室还没有成为盗贼的目标，因而相对来说安全措施较差，于是损失上升很快。

【答案解析】[要点]这是一个并列主从复合句，前后两个句子由and连接。句架是...the problem was the theft...,and be cause most of these were based in offices which...，and thus had relatively poor security，losses mounted very quickly。在后面的句子里，主句是losses mounted...，前面是because引导的原因状语从句，该从句有两个并列的谓语；which引导定语从句，修饰offices。句中PC指个人电脑；security在这里是“安全防范措施”的意思。