Is it possible for a virus on 3G card?

This might be a silly question. I did a google search and not much turned up so maybe that answers my question but still I thought let me just ask.

A person sent me their laptop which was infected with lots of malware...it was a bit crazy. I managed to clear all viruses and fix the reg problems they caused. I now want to send the laptop back but am worried this person goes and infects it again.

When discussing this over the phone with the person she says that she has noticed every PC she has plugged her 3G card in has started causing problems

Now initially I thought well these cards are or should be write protected meaning no virus can get onto it.

but..............Is it at all possible that a virus can still get onto these 3G USB flash-stick/data card type modems????

Otherwise maybe she is just visiting a certain website all the time and I will have to get to the bottom of this

What about installing antivirus on her machine?

What 3G modem/router is she using?

And if it's an USB thingy with memory for user files, then it should be scanned as it will cause further infection.

She has Mcafee on her PC. It is company policy/software standard and can't be changed unfortunately and it is the most k*k anti-virus under the sun IMO as it has only saved me from viruses about 10% of the time if even. Better than nothing I guess :/

It is those USB modems that are almost like memory keys and have the software built-in.