Writing has always been considered an important literacy skill for foreign/second language learners. The Internet provides such unique applications for the writing skill as weblogs, wikis, and social networking websites. Up to now researchers have put their focus on the learners’ performances in the traditional paper and pencil environment or wikis and blogs it is time to also consider learners’ performances in the social networking websites. In this respect the purposes of the present study were to (a) to identify the most frequent Iranian learners’ errors in the virtual environment of social networking websites, and (b) compare the learners’ performances in the traditional and virtual environments. With respect to the requirements of the research questions, this study had two phases of data collection. For the first phase, the researchers selected 30 Iranians, male and female, aged 18 to 21 from one of the social networking websites and collected a 3200-word corpus from among their comments and wall posts. All of the learners were students of Computer Engineering and IT. For the second phase of the study, another 3200-word corpus were collected from 30 Iranians, male and female, aged 18 to 21, who were studying Computer Engineering and IT at Sheikhbahaee University. They were asked to write an essay on an assigned topic. The analysis of the results revealed that three most Iranian participants’ errors were verb forms, diction, and prepositions in the virtual environment. Based on the results of the t-test, Mann-Whitney, and Chi-square tests interesting similarities and differences were observed within and between error groups in each corpus.